These are good questions to start with. I'd recommend rephrasing the first question to "How likely would you be to use this app?" (subtle but important difference - it can be "helpful" but they may not use it). And rephrasing the second to "How much would you be willing to pay for this app?" (again, idea vs. intent).

You can also get a sense for Net Promoter Score (NPS) by asking "On a scale of 1 to 10, how likely would you be to recommend this app to a friend?" (Learn how to calculate NPS here: http://www.netpromoter.com/why-net-promoter/know)

First of all, the questions asked by you is more about validating your product than market. Hence, you need to be clear with the objective of the survey. Do you want to validate the market or the product?

If you want to assess the need of your product then you need to undertake a "Need Assessment" survey.

If you're struggling with pricing your product or adding feature (s) per pricing plan then you need to analyze the market/competition to be able to benchmark against.

Is there anything specific you're looking at? Feel free to reach out with more clarity to get clarity. All the best!!

Great answers so far but I wanted to add another perspective:

One of the assumptions that is core to surveys being valuable is that answering "I want this" and putting in your credit card are two different things. In reality, there is quite some difference.

In order to truly tell whether an offer resonates, nothing substitutes for the real thing. This is sort of off the beaten path for lean startup but has been used in quantitative direct response marketing effectively for decades.

You could easily be getting in front of real customers and following their feet, not their lips with the budget you have allocated for this survey. At .95/response you could most likely get more respondents as well.

By split testing - you can get insight into key benefits, price points and anything else you could possibly want with REAL intent being measured by conversion.

In addition, you can build a pre-order list and get a few steps ahead on your customer acqusition channel at the same time.

You'll need a bit of knowledge in CRO, advertising and copywriting but for something like this it's all 101 level stuff. Give me a shout if you're interested and need a hand!

It is essential to understand that a product should go through Market Validation Survey for these questions are too abstract in nature and does not reflect the true nature of the product you are about to launch. These surveys are highly essential. Keep the following in mind:
1. Create clear objectives:
1. Understand if its core offering is priced appropriately
a) The data (output of answer options) needs to allow Modify to clearly indicate where people think the current pricing is too high, too low, or about right
b) Understand brand recognition (unaided and aided) in the market to get a sense of how they should position themselves in marketing/PR (and be able to cut this data based on watch/accessory budgets and demographics)
2. Find out which types of customers are most likely to purchase its product
a) Where are the demographic sweet spots in terms of pricing and interest?
3. Get custom market stats it can use to build a TAM (total addressable market), sanity check its market understanding and build customized data for presentations, potentially for fundraising
a. How frequently do people buy watches?
b. About how much do people spend on watches?
c. How likely are people to purchase a watch online?
4. Understand key info around its new watch subscription offering to validate whether this is a business initiative it should focus on
a) Are people interested in a subscription offering that allows them to get new watches on a regular or semi-regular basis?
b) How much should they charge?
c) How frequently do people want new watches?

2. Determine your target audience: For Modify, they are asking questions related to watches. Pretty much everyone in the world has one or wears one, particularly those who can afford Internet connectivity (project sample base/target population).
Sample size: 1,000 people should be enough to give us a sample size with high confidence
Targeting: US, gender balanced. We want this to look pretty like the US population. Everyone is a potential watch buyer that Modify wants to hear from.
3. Create a great survey:
Following is a sample survey of how Modify can achieve its feedback objectives by eliciting actionable data to help inform the business decisions it is considering. The survey questions are shown below without the multiple-choice options for answers belong to a Watch company, this is to give you an idea how to frame your questions.

WATCH BASICS
1) Do you wear a watch on a daily or frequent basis?
2) Approximately how many watches do you own?
3) How often do you purchase watches?
WATCH PRICING AND PURCHASING
4) On average, how much do you spend when purchasing a new watch?
5) Have you ever purchased a watch online?
6) How did you purchase your last watch?
7) When you think of watch brands, which brands come to mind?
AIDED BRAND AWARENESS
8.) Which of the following watch brands are you familiar with? (Select all that apply.) [randomize]
• Casio, Modify, Rolex, Omega, Cartier, Tag Heuer, Movado, Diesel, Timex, Starck, Fossil, none of the above, Other (please specify)
9) Based on the information above, how likely would you be to purchase a Modify Watch?
10) About how much would you be willing to pay for a Modify Watch face and band?
MODIFY PRICING
11) Modify prices its watches based on the price of a watch face ($25) and the price of a band ($15). The bands and faces are interchangeable, so various combinations can be created for customers who purchase multiple bands and/or faces. Do you think that Modify watch face and band pricing is expensive or inexpensive?
12) Modify has recently created a subscription offering where customers can sign up for a subscription to receive new watches periodically. Customers also receive a discount on each watch as part of the subscription package. How likely would you be to sign up for a subscription offering to receive new watches periodically at discounted prices?
INTERESTED IN SUBSCRIPTION
13) If you were to sign up for a watch subscription package, how frequently would you want to receive new watches?
14) If you were to sign up for a watch subscription package, who would you like to choose the watches you receive?
15) How much of a discount off the base pricing for watch faces ($25) and bands ($15) would you require to sign up for a watch subscription package?
4. Uncovering Critical Insights:
After launching the survey, results came in immediately. After just a couple of days, Modify was ready to begin analysing its data, finding the key insights they needed to act on and help grow their business. Since Modify used sound survey creation principles, the results and data are actionable and a key step in the process could begin. The topic we at SurveyMonkey ask a lot of customers or potential customers, and even ourselves, before, during and after running projects is, “Now that you have answers and data, what are you going to do with it? So, how is Modify going to use this data to help grow their business and make better decisions?
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath