I think there are two very different things you want. One is test our application on a great number of devices and Android version combinations. This is to make sure your app runs smoothly on all the environments you need. The other is a way to collect usage data, core dumps and physicians feedback.

The first thing can be accomplished with a device farm and automated tests. Xamarin Test Cloud ( http://xamarin.com/test-cloud ) allows you to to automated testing on about 600 devices. There are other providers but this is the one that I would use and trust the provider.

The second thing can be accomplished using many tools, even the ones you already use, e.g., trello or slack, for feedbacks. I have seen many companies go for beta releases on Google Play linked with private Google+ groups for beta testers.

For crash dumps and usage monitoring you can use Twitter Clashalytics ( http://try.crashlytics.com/ ) or other tools like:

* http://www.mobtest.com/
* http://ubertesters.com/
* http://hockeyapp.net/
* http://www.centercode.com/

Keep in mind that regardless of the tool you choose you will need to setup each device and register it on iTunes Connect. Note also that there are limits:

* 100 users/devices per Developer Apple ID (Apple seems to me migrating to a 200 devices limit)
* Devices can be removed/replaced just once each membership year
* A time limit of 90 days

There are some alternatives:

* Ad-hoc installation (needs physical access to the device)
* Testflight (https://testflightapp.com/) the one I use and recommend +++
* Pieceable (https://www.pieceable.com/) lets you test over the web browser
* AppHance (http://www.utest.com/apphance) is a TestFlight like service
* HockeyKit (https://github.com/TheRealKerni/HockeyKit) is an opensource stack to host beta apps on the web (still needs the device registration on iTunes Connect)
* HockeyApp (http://hockeyapp.net/features/) an TestFlight like service

Most of the successful consulting business that I know of start their marketing efforts by building trust and being acknowledged as reference on their fields. They do lectures, participate and organize events and write articles to newspapers, magazines and respected websites/blogs.

At any time most of the income will be generated by 20% of the contracts and 20% of the contracts will consume most of the time the consultants have. The big secret is to align both 20% (to have the most of the income generated by the 20% that consumes most of the time) so that you don't waste most of your time on the clients that generate least results.

The charges usually will be using one of this three models:
* Per hour rates (sometimes with different rates for each kind of work/skill)
* Per result rates (an amount of the result increase or the result economy/decrease, depending on the type of the action)
* Per action rates (fixed amounts for specific actions/efforts)

If you want more examples, call me.

If you are aiming on iOS and Android with Windows Phone 7/8 as a plus you should use C# as the language and Xamarin Studio as the IDE/Framework. You may also choose to use Visual Studio on Windows as an option.

Take a look on their website: http://www.xamarin.com

Even Microsoft is using Xamarin to build iOS applications and they have over 400k developers using it. Your application will be native (compiled to the platform you choose) and you are able to use all the native libraries, widgets and UI parts.

You will need a cross-platform architecture to be able to reuse code among platforms and using Xamarin you may be able to reuse more than 50-60% of your C# code among platforms.

This solution may render the same experience on the devices as on the website, but it enables your applications to deliver much more performance and features than any HTML5 solution. Facebook went from HTML5 to native applications due to performance and user experience limitations (gestures and other platform features are not present using HTML5).

Do you know how Mailbox App did it?

They had a closed beta but they hard a website, a landing page and an iOS Application that enabled people to register in queue waiting for a slot be to accepted into the closed beta.

People had a newsletter delivered to them and were able to share and invite others (this social actions pulled them ahead on the queue). This way people could interact, share and receive newsletters on Mailbox App even though they were not included on the closed beta. It was a successful strategy and other companies did it also with success.

Read this article to know more about it and how you may be able to do it also:
http://techcrunch.com/2013/04/01/queueing-theory-lets-any-app-offer-a-mailbox-like-reservation-system-even-if-its-just-for-building-buzz/

I think that image file URLs are best and this is why:

* Base64 Strings and Files might have the same quality if your string is a encoded version of your image file
* Base64 Strings are much bigger than binary files (Usually 33% bigger) - http://davidbcalhoun.com/2011/when-to-base64-encode-images-and-when-not-to
* You only need Base64 when delivering the image using channels that are 7-bit encoded like emails, text files, CSS, HTML or other medium that only allows lower ascii characters.
* Gzipped images have the shortest size and pure binary image files are the faster to decode/display

Have you tried AdWords and a website/landing page for you or your business?

I know a company in Brazil that is doing exactly this:

* They have a website/landing page setup that explains how they charge for the application and has a call-to-action button to ask for an evaluation of the project the client have
* They have thought and described a way to evaluate projects roughly so that the client may have an idea of time / costs of the project
* Their website has images of applications they have developed before in a portfolio

They are doing great, actually they have more people asking them projects than they are able to develop and they started rejecting offers.