Moving dozens of existing standalone retail sites to one central inventory database: what should I know going in? [closed]

Question

This will be the first project of this scale that I have attempted, and the first time I have run a website at all (much less dozens) using an off-site database. In particular, I'd like to know:

1. what sort of optimizations I should read up on to make this run as smoothly as possible?

2. any pitfalls/gotchas wiser, more experienced folk are aware of I should be on the lookout for, and

3. what damage-control and preventative measures I should take against the nightmare scenario of the main server (hosting the database) having an outage, grinding over 100 websites to a halt (because they have no access to the product data).