Hi Mike. Welcome to this great forum.
This kind of question gets asked all the time on every gun board on the net.
Hopefully this response is helpful to you, as it is the advice that I wish I had received before spending more money than I needed to:
1) Having $900 is a great budget to work with, and there are many very good options available at that price, including most of the major brands.
2) You do not yet know if the RIA, or any other pistol you buy is reliable until you shoot it, and shoot it a lot. You will learn more with a $500 pistol and $400 worth of ammo than anything else you can do. The bottom line, honestly, is this: If you want to learn more, shoot more.
3) Stop thinking about modifications unless you can clearly understand why you are making that particular modification to that particular pistol. This will save you more time and money than anything else I can think of. For example, you use your budget on a basic pistol, and a case (or so) of ammo... you then shoot hundreds and hundreds of rounds through it.. . After doing this you can tell us what it needs. Most will need nothing.
You can worry about the upgrades and nice-to-haves one piece at a time, this way you will actually know if the modification made a difference. (always remember that you will never recover the $ from the modifications you make- unless the modifications were made by a big name custom shop on a big name base pistol i.e. Colt/Springfield/...)
While I know next to nothing about RIA pistols first hand, I hear that they are a very good value. If it was me- at that budget- I would find a used one from a more mainstream brand, like Colt or Springfield simply because it would hold it's value much better.
Hope this helps.
Moses