I don't have any experience with Wizardry clones so I am curious how is dual classing usefull and when should be made. I don't mean necessarily for this game, but in general. I'm thinking of starting one of these: Wizardry 6, Wizardry Empire II, Elminage Gothic or SoSC. From what I saw on this forum, multiclassing seems useful to gain mostly buff/debuff spells. Aren't characters with only the original class better than multiclassed? I'm thinking they should have better skills/spells at higher levels than multiclassed chars. Multiclassing seems to involve having some metaknowledge about the game and I think this is why I'm not excited about it.
start with ELMINAGE: ORIGINAL. it is available in english for PSP. you can buy it or you can download an .ISO of it and play it on the PPSSPP emulator. your choice.
gothic is much more hard-core than elminage: original... but then again, i started with Gothic. So scratch what i just said: go play elminage: gothic.
after you've gotten your feet wet with any of the elminage games i recommend downloading the SUPER NINTENDO ROM game titled "WIZARDRY - STORY OF LLYLGAMYN".
it is a SUPER NINTENDO ROM GAME which features much-updated remakes of the first three Wizardry games, i.e. wiz 1, 2 and 3.
alternatively i also recommend the EXACT SAME thing, but on ps1. google/download an .ISO of the ps1 GAME DISC titled "WIZARDRY - AGE OF LLYLGAMYN" which contains POLYGONAL remakes of the first three Wizardry games, i.e. wiz 1, 2 and 3.
The SUPER NES ROM GAME version features beautiful, unbelievably gorgeous SPRITE ART and is probably one of the most visually pleasing games you will ever play. however the ps1 disc collection(s) feature much more accurate GAME SCRIPTS. the actual DUNGEONS are exactly the same.
BOTH PS1 AND ALSO THE SNES VERSIONS are "easier" than the original APPLE II releases, and also the DOS releases. This translates into ever so slightly altered encounter ratios and variables and eeeeeeeveeeer so slightly "tweaked" loot drop tables.
however either of the versions will kick your fucking ass, guaranteed, and you will love every second.
after all that then you are ready for wizardry empire 2. that game is harder (but ever so much more rewarding!) than either the elminage games or the first 3 Wizardry games (remakes or originals).
In-between all this also remember to download and play the Wizardry 5 16-bit remake on the SNES and polygonal remake on the PS1. the exact same caveats apply.
now as for your question about multiclassing: completely up to you. there are no hard and fast rules. all Wizardry games, and i mean the original ones on apple ii and DOS, and ALL OTHER WIZ-CLONES, are 100% beatable without any problems whatsoever even if you never ever change classes.
play the games first and experiment. have fun. let the games themselves shape your opinions.
other options that you should play but not now and only after having played the games i just listed:
class of heroes series on psp
generation xth: code hazard on windows pc
paper sorcerer on windows pc
wizardry 4, either original release or the ps1 remake.
stranger in sword city for windows pc.
wizardry gaiden 6: the prisoner of the battles for ps2 (japanese game but it was released with english-language options)
EDIT: ohh yeah! wiz 6... well whenever you find yourself bored or whatever some rainy day go ahead and either play the original DOS release or play the SNES remake. it's an alright RPG but not a very good Wizardry game. It was the beginning of the end for the Wiz series, with 7 and 8 departing further and further away from core Wizardry design. that said Wiz 8 for PC is a better game *overall* than either wiz 6 or 7.