There are some class balance changes, mainly:
1) Ultima Boost: +100 ATP, +100 DFP, +100 MST, +10 ATA and +30 EVP MAX stat boost for every class.
This slightly impacts how each class can be maxed out with their stats (or cannot be maxed out, for that matter), although it isn't a huge deal if you just want to play and enjoy the game.
2) Class weapon changes
Ultima has quite a few new items. There are several weapon types that all classes can use in ultima which were restricted to certain classes in the original game. You may see forces running around with bazookas, twin swords, rifles, etc., hunters with launchers, rifles, or shots, etc. These weapons drastically change the gameplay for some classes, especially for melee forces and to a lesser degree, hunters and rangers.
There are also some new weapons that are very strong and are either class-specific or sex-specific, so some male hunters and rangers can have a leg-up in some areas over females with items like Psycho Ravens, while females may have more alternatives for strong gear (Sue's coat, Kroe's sweater, safety heart/sweetheart items, etc). Forces also have more access to strong weapons, so playstyles like melee force are much more viable on this server.
Weapons without a special (like most of the rianov rifles, yasminkov series weapons and several other weapons) can have a special put on them if you pay 10 donation tickets to a GM, so some classes that can utilize these weapons receive a buff (demon/charge yasminkov 9000s, for example, can help rangers tear through certain high hp/DFP monsters)
3) Monster stat buffs (mostly on Ultimate difficulty and especially in Episode II)
The main stats (in my opinion) that effect class balance the most are the increased monster elemental resistances and EVP. Because of these enemy boosts, forces have a very difficult time using techniques as a means to kill enemies on Episode I & II in ultimate, but they still do a good job with nuking on Episode IV. Also, classes with a low max ATA like Fomar and Hucast need a good bit of hit% on their weapons in order to hit monsters reliably. Even with really high hit weapons and max ATA, Fomar can still miss a good amount in Episode II. As a result, classes with naturally high ATA are a little bit easier to play and tend to have smoother gameplay on ultimate difficulty (in my opinion). Also, nuking techs on non-force characters are pretty obsolete if you want to use them for damage on higher difficulties, except for a couple niche purposes.
There have not been any major class rebalances (like drastically changing the stat proportions of a specific class) as far as I know, so generally each class holds a similar position in relative strength that it did in the original PSO. Hucasts still hit like trucks, Ramarl is still a great solo class, etc. I'd also say that traps are more useful on ultima because some of the endgame quests have very high monster density, so crowd control options like freeze traps become even more useful (although they were VERY useful in original PSO as well). While some classes might be a bit stronger than others, every class is still good enough to get the job done, so you should pick the class that looks the best and has the type of gameplay you prefer!
Fomar has always been my favorite class, and their gameplay is really fun in Ultima. I'd suggest saving 5-10pds and buying a Godric's Cloak off of another player when you get the chance. It's an armor specific only to Fomar and its easily one of the top two best armors for the class; it will literally carry you all the way to lvl 200.
Once you get Godrics, I'd probably invest in a cheap Lindcray, Rico's Parasol, Banana cannon, and Lame d'argent/Hundred souls as well as a Heavenly/battle and an ADEPT. If you can afford it, I'd also consider looking into getting a Hylian shield when you have the opportunity.
I'd also farm some Ep. IV on normal/hard difficulty to get some Photon Crystals, which you can use to play the Black Papers Deal 2 quest to get a Smartlink, which will help your accuracy with ranged weapons significantly. I would also spend some time playing the Ep. IV solo quest "Restless Lion" to get some starter weapons with good specials (demons, hell, charge, etc) and high percentages and hit. The weapons that you take from the dead bodies of the enemy hunters have a very high chance to have percentages and hit, and they always have the best type of specials of their respective category (Blizzard, demons, hell, etc)
Forces in general have the ability to automatically be worth taking in a party simply because a high level shifta, deband, jellen, and zalure drastically improves the safety and damage output of a team, so you'll always be an asset to your group, even if your gear isn't very good. Jellen/Zalure are also great ways to "tag" monsters so that you receive a lot of experience in teamplay. That being said, because of Fomar's low ATA and the force playstyle in general, you're going to have a lot of work ahead of you to get those really good items which make the class feel powerful in its own right.