For An Online Store?

I am currently shopping for web hosting for an online store (that would provide software - mostly automatically downloadable upon payment).

My estimates for initial operation of my web/online store are:

Storage: (10MB/app x 50 apps) + 50MB overhead = 550 MB
Monthly transfer: 5000 purchases/month x 10MB/app = 10 GB
Number of email accounts: up to 10

By "initial" I mean first year, not first month.

My intent is to develop my own osCommerce based web store for downloadable software that I develop. PHP and MySQL support are must. My estimates are not carved in stone. In the beginning I will certainly use much less "monthly transfer" than I specified and in the long term I hope to be using much more "monthly transfer" (as marketing evolves and the business becomes more established)...

The most important factors to me are (in the following order):

1) Reliability (up-time, security)
2) Tech support
3) Expandability (room to grow)

The company that registered my domain name provides web hosting with much more than I initially need (5GB space, 250GB transfer, 50 email accounts) for under $3 a month.

This is a price that I can afford. However, I am not sure whether it is a good idea to have both the web hosting and domain registration provided by the same company? Any opinions/comments you have about this? Is my doubt in this regard unfounded?

Secondly, is there some independent source (user/customer reviews OK) that compares the reliability of web hosting providers? (I would have given the name of my registrar here but I am unsure whether this would constitute advertising. If mentioning names or asking for references is allowed please let me know and I will post it here so that I can get your opinions about it).

Thirdly, is there any significance for where, geographically, the actual servers are located? Main consideration is access speed for customers...