Hi, first of all welcome back!
a quick update of whats been added to the game can be seen here:
A Summary for Returning Players – Ultima Online
Theres alot of text but you dont need to know all, even alot of active players dont have the full overview
I would also recomend
UOGuide - the Ultima Online Encyclopedia as a good reference, if you need to look up items, dungeons, cities, vvv(pvp system) or anything else.
When it comes to specific items to wear in pvp or pve, it doenst matter that much. Theres so many items around now theres like 999 ways to make a suit.
Most is to focus on reaching the hard caps, like 45hci, 45dci, 40lmc, 100% lrc, 2 fasterCast and 6 fasterCastRecovery. As a mage, in pvp and PvE.
If this sounds foreign to you, you can look it up on uoguide with the search button top right
I would also recomend using item insurance in your character context menu (click yourselves) so you dont lose items if you die. (this requires gold in bank btw)
Any item with the property (Cursed) will drop if you die, its a negative mod on an item, basically useless item.
As for skills a mage usually have magery, eval, resisting spells, wrestling and extra skills like inscription/parrying/ spellweaving, some have necro/spirit speak, its alot of combinations espessially in PvP. If you havent played for a while I wouldnt recomend pvp or felucca at first.
good luck and just ask questions here or in general chat and we will answer them