Using a foundation is the best way to develop VFP applications. It is best to purchase an application foundation written and supported by someone else. Developers do not have time to write foundations, and develop applications, unless the client is paying for such a service. You are taking the best path, and the more questions you ask, the better.
You may or may not have looked into:

www.flashusa && Codebook (basis of VFE and Mere Mortals)
www.maxlink.com && Visual MaxFrame Professional
www.promatrix.com && Visual ProMatrix

What ever product you select, will require learning how to use the tool. This will take time, regardless of what someones marketing department has writen.
Some suggestions to ask before you buy:
1. Is there an InterNet web site that allows framework users to assist each other? How much activity on the user forum? Quality of questions and answers?
2. What is the fee for professional assistance, if available and necessary?
3. Can you use SQL pass thru as well as views?
4. Quality of tutorial, and on line help files?
5. Examples of application elements (forms, security, etc.)
6. Is there a user group in your area for the framework you have chosen, or at least some fellow developers?

The above frameworks if used on a CPU with a speed of at least 200Mhz, will work well, as far as the user is concerned.

How large is large (data sets)? If you are going client/server, you have to balance the size of a data set vs network considerations (bandwidth, users, traffic, etc.) I have used backends with tables of 8 to 12 Gb, and returned record sets of 2500 records, on a 100T system. It only takes a few seconds to obtain record sets of this size. If you are talking about record sets of 100,000 rcords, you will slow down the system to a crawl.

Tom