tried to edit, was timed out.
summing up? if that's possible..(this can be a rather involved subject)
lets just say a few things to consider when moving hosts..
Disc size is not important unless you truly need a zillion gigabytes of space..
how big is your website? 600 html pages, that's nothing.
However, if you have a big movie and photo gallery, you just might need 10 gigs of space or get a CDN(content delivery network) to help hold and deliver the media for the pages.
files
Be sure to grab a copy of everything from the server in advance of any change.. including a database dump, if used.
Email could be a small issue when changing hosts if you were using the hosts' web mail and have saved mail you need to keep.
The Domain (To me, this is the big one)
The domain being in a place where you can control it after leaving the old host, if you registered it through your hosting account.
** Many times you can still control the domain separately when leaving a host if the host is a domain reseller. Your domain would then be controlled by accessing the reseller site directly with your original user name and password from the hosting account.
The rule is,, You own it, you control it, you can transfer it anytime you want, you set the name servers to what you need at that time.
The rest of it is not a problem,,
The thing is that most hosts are running a shared environment that can be slow at high demand times, but will still serve a normal business web site just fine.. Most of my sites for small business run straight html/php.. and most of the ones using a database, are running a file based cache to make up for the delay from the shared sql server.
If you need a fast database, move up to a VPS or share a server with others.
The must haves are really basic stuff.. but look and make sure anyway,
--some hosts do not have htaccess-- yes, it can be a real pain-in-the-uknow
htaccess
addon domains to account, I like at least 5 but no limit is better..
domain pointer
email
ftp accounts
error log access
stats
mysql database, or another acceptable db (one is all you need, sql has no table limit)
cgi
php
php.ini (access to set things the way you want)
sub-domains -optional, but can be a blessing when developing a fresh site or separating departments.
I know I missed some stuff,, help me out eric...
I think Eric would be a good host especially if you need a knowledgeable person on your side so your site would be done right.