Just to understand better - are you building a game/app? or are you building a business with recurring revenues (like say SaaS)? The answer varies based on this.
Also, are you looking at the data specifically for users you are getting from just this campaign or just your overall revenue analysis?
Sorry I'm asking more questions, but the answer depends on these questions.
You should be careful to map the spend to its own results to judge if its ok to keep spending in the manner. Only that can tell you if its worth spending unless there are other benefits to the advertising spend (higher rankings on appstore for a game for instance)

Check out NFNLabs/Effectworks(nfnlabs.in). They built the demonstrate app which is pretty well designed and executed and has been featured in a tonne of places for being a nicely built app. (Full disclosure: these guys are good friends. But I do really like their work :) )
You can also reach out to contractIQ who will help you find the right folks based on your needs.

I am guessing you have a good idea of who your likely customers could be - maybe you have an idea of who your marquee customers could be, and a list of smaller companies that could be your early adopters.

The best way is to reach out to these companies and talk to them and sign them up as beta customers for when you launch.

Of course, you could also post on forums like Hacker News or forums that are relevant to your customers to attract their attention. However, I feel a real conversation is the best way to get a feel for who will sign up as an active beta user.

Reach out via people in your network, or request for a short call to get feedback from your potential customers and try to turn them into beta users.

You are right that the range is wide. You need to figure what are good values to have for your category. Also, you can focus on the trend (is your DAU/MAU increasing vs decreasing after you make changes) even if benchmarking is tough.

Unless your app is adding a huge number of users every day (which can skew DAU/MAU), you can trust the ratio as a good indication of how engaged your users are.

For games, DAU/MAU of ~20-30% is considered to be pretty good.

For social apps, like a messenger app, a successful one would have a DAU/MAU closer to 50%.

In general most apps struggle to get to DAU/MAU of 20% or more.

Make sure you have the right definition of who is an active user for your app, and get a good sense of what % of users are actually using your app every day.

Happy to discuss what is a good benchmark for your specific app depending on what it does.

A friend runs a site called "Contract IQ" (www.contractiq.com). Suggest you list yourself there and find other such avenues to showcase your prior work so clients can find you!

I am assuming your question is more pertaining to empowering and motivating (rather than hiring).
I can outline some of the practices I have seen really result in high motivation and sense of ownership among engineering teams:
* Empathize - Your engineering team will work well and be more motivated if they see you as one of them rather than a person who doesn't understand their function. Show your geeky side to them, and show that you understand their thought process and drivers.
* Pick their brain on big and small decisions (roadmap, usability, whatever it is) - Product teams value being heard. The more you position yourself as someone who is WANTS to listen, is keen to have their inputs, you will be surprised at how involved they can get, and also how you can actually tap into a lot of smart ideas/thoughts from them that you can develop on.
* Take care to explain - show how you arrive at decisions. Share your research, competitive analysis, and even your thought process on arriving at a feature set or list of things for a release. Its stuff you would have worked on anyway - so no harm sharing with more eyes!
* Share customer feedback - nothing motivates your engineers than a positive interaction with a customer. Get them to see customer feedback. Have them sit in and observe some of the usability studies. (B2B - have them see you do some demos or do a successful sales pitch)
* Send out interesting articles, insights, business and tech articles with your comments/highlights to them on a regular basis (maybe twice a week?) - maybe even some analysis you did on competition or customer feedback
* Engineers like working with people they feel are competent and complement the work they are doing to build a great product. So make sure they see how everyone else around them is also doing a good job and adding value and contributing to the success of the product.
* Be transparent about the product/business - Make them feel they are responsible and involved in the business, not just technology. I've seen engineering teams happy about their annual goals having components relating to making revenues, keeping customers happy, or reducing costs. If they are enthused about the business as a whole, they will be more motivated with their engineering efforts
* Have a mix of little experiments, R&D, attending to engineering debt, in addition to bug fixes and new features that each engineer gets to spend some time on (based on their interest)
* Finally get to know each of your engineers personally, and be aware of what their priorities are. Each of us has different motivations in life, so there is no silver bullet to motivate people. When they know you care for them, they are more motivated :).

There are different approaches that work for different people based on your comfort and personality. I am highly uncomfortable confronting people. So I try to influence people to see the point over a period of time. BTW, you should probably read the book "Influence without Authority".

Most people respond well when you make problems to be about the company, and about learning/trying out new things, rather than about a person and their ways.

"Hey! I am keen to see how using a framework can help our product. I am looking at some great examples and their cited benefits, and was wondering if we could manage to shift towards using a framework over the next quarter. I know there is a lot on our plate, but I'd be glad to champion this effort. Won't let you down. What do you think?"

I've seen some people use "insult into action" methods as well - where you question someone casually(should not be seen as harmful) in a public situation. Like in front of the CTO, ask an innocent question "Hey TeamLead. Why can't we use XZY design pattern for this? Is there a reason we never use design patterns? I'm sure you have a reason and I'd love to understand."

A good way to start would be to first define metrics to identify who are your happy users, and engage with them to let them know you care about adding value to their experiences.

For simplicity, start by looking at your most engaged users (e.g.:spent over 10 minutes per day in your app, for 5 out of the last 10 days). Reach out to these users to understand (a) what they like about your app, and (b) how the app could delight them further. Offer them a promotion/reward for helping you with feedback. They will see you are keen on keeping the relationship going and feel part of any success you have.

The same could also work for your most unhappy users. Ping users who aren't engaging with you, have left you bad feedback, to find how you can make yourself relevant to them, and what they are missing out on. You may be surprised to see how, once you start listening to them, they can become your most vocal evangelists.