Not sure if it's legal or not to have it loaded on multiple computers, you would have to read the EULA to be sure. With that said, it will load on multiple machines. It will load without the disks just by downloading the patcher, but then you're talking about alot of hours of patching, and days to weeks if on dial-up.
Not really compatible, but it will run on vista, sometimes without any adjustments. Sometimes you need to make a few. There are several threads on the first page of this forum with links and info on what adjustments may be required.
You can not change your characters class (occupation / job, class is the term used in EQ). There is the option to shroud to various NPC races and classes however, but this is not the same as changing your characters class. This option is intended to allow players to lower there level and play with there friends who aren't upto their characters level range. It is often used for many things, the most common of which is becoming a rogue (thief) in order to be able to sneak / hide past many types of creatures, and/or pick locks.
Also, you get eight character slots per server per account, so you can have characters of eight different classes on just a single server and single account.
There are many threads on which servers to play on. Some of the most common suggestions are Combine (Progressive server), Zek (PvP but you mentioned not being interested in it, and also, PvP has some different rules, etc.), Stromm (for many years was labeled the newbie server), Tunare, Firioni Vie (Roleplaying server with some different rules).
75 is the highest attainable level at the moment, going up to 80 with the next expansion in November. At 51, you can start Alternate Advancement (AA) with most classes at max level and all expansions being able to get more than 2000 AA before becoming maxed. If you're worried about maxing out, that is unlikely o happen even with hardcore play and non-stop grinding within a year.
Yther Ore.
Edited to fix grammar, but I probably still have some more :D
Edited, Jun 18th 2007 2:47pm by Yther