First and foremeost welcome to Ultima!
Now to try and answer you questions...
Q Have there been any changes to monster stats? I am playing one person mode in hard forest, lvl 45 humar, really struggling... maybe its just cause I havent played for a long time? I am sure I used to do it at lvl 30 odd.
A Might just be the gear you currently have and mag being low level. In solo mode monsters are weaker compared to normal online. Also to elaborate there is a boost to the classes of +100 ATP, +100 DFP, +100 MST, +10 ATA, EVP I cant recall and LCK remains the same at 100.
Q Any changes to drop files from the originals?
A Some drops have been altered. Here is the drop chart (Its located at the top of the page) http://www.phantasystaronline.net/droptable.php
Q My game crashes randomly - from opening the armour shop to putting meseta in the bank, are these known issues, any fixes?
A Crashes do occur but not frequently. Try and avoid keeping inventory full at 30/30 as Radezz stated. Please read the pinned posts under Bugs and Crashes for further tips!
Q Any recommended quests that are new to this server?
A There are several quests. Lost Riot Raygun Ep.II, MA4DMD Ep.IV just to name. You can find more info about quests by using the search functions.
Hope that helps.