Hello,
I can't find any option to re-use my endgame BT2 characters when starting BT3 !
the Autosave is overwritten (no other option possible) and then I have only the default rooster and members.

Go into any of the Adventurer's Guilds in BT2. There should be an option to transfer your characters over to BT3 there. You can do a full power transfer (characters retain their levels) a mid-power transfer (characters at LVL 13 or so, I believe) and a newbie transfer (characters reset to LVL 1) They get to keep their equipment in each of these cases.

After you pass the starter dungeon in BT3, your non-mage characters are boosted to LVL 35, and your mages are all sent to Archmage LVL 5. That's mainly to give you enough XP to allow you to change one of your mages to a Chronomancer, which will let you get to the other realms in the game.

Out of curiosity, what happens to Chronomancers and (if you somehow have any in your party) Geomancers at this point?

(In classic versions, lesser casters become level 1 Archmages while Archmages, Chronomancers, and Geomancers get boosted to level 35. However, a character can only get the boost once, so getting the boost for a Geomancer requires not getting the boost for that character right away, which is not something a typical player will think to do.)

(Also, I read that the mid-level transfer caps level at 24 when transferring to BT2 and 33 when transferring to BT3.)

(Also, apparently you need to beat the game before you can transfer to the next one. Personally, I don't like this change.)

You can't get out of Skara Brae until you clear the starter dungeon, so no Geomancers are possible. Likewise, the Old Man at the Review Board won't allow any of your Archmages to change class into Chronomancers until you go through the starter dungeon. I'm assuming you can only get the boost once (I have not tried to go through the Starter Dungeon again) so you don't get an easy boost to any new characters to LVL 35 just by going through there with a couple of archmages and four new characters.

Not sure if I like that change (in the original, you could change characters to chronomancers as soon as you meet the requirements (which I usually reach right before the boss for the Preclusion spell), so you could reasonably have a Chronomancer at that point, and you could also skip the starter dungeon entirely if you are strong enough).

(Also, it should, of course, be possible to hack the save file to turn a character into a Geomancer at any point; might even be possible in BT1 or BT2, though note that the damage spells you learn aren't balanced for those games (though the later part of BT2 features enemies with enough HP to survive even the likes of Jolt Bolt).)

Yeah, I'd forgotten just how much health some of these enemies have in BT3. Even in Arboria, I'm running into some critters that take MAMA from both my Archmages to kill off.

I think they prevented that just so you could not have a LVL 35 Chronomancer to go into the game. As for hacking the data file, if you're going to do that to give yourself a Geomancer, then you can certainly give them enough XP to reach LVL 35 at the start of the game. :)

Sometimes I like to study the game and see how it behaves under unusual circumstances.

One of my favorite things to do in classic versions of Bard's Tale 3, for example, is to form a party containing only monsters, then drop every monster from the party. For whatever reason, and unlike Bard's Tale 2 (which gives you an instant game over if you try this), in BT3 you can actually wander around with nobody in the party. Of course, once you get into a battle, it's game over if you can't run away, but an enemy might try to attack one of your party members (who?).

Anyway, if I were to hack the game for real, I would rather do something more fun, like giving a monster party member the ability to cast spells such as DIVA or NUKE. (I remember, in the DOS version of BT2, fighting the final boss with a monster capable of casting SPBI and the Dreamspell (make sure to set the Dreamspell flag if you're using the DOS version or else the spell will fizzle!) for fun; of course, I had to make the monster the Destiny Knight for this to work.)

By the way, BT3 does have one special party member you can get legitimately that is capable of casting Heal All; that can be quite handy if you need to recover from a party wipe.

(Also, classic versions of BT3 have a monster that can cast Mage Flame; I highly suspect this is a bug, seeing as how Mage Flame has an index of 0. I note that the remaster's changelog mentiones an enemy (not in BT3) casting Mage Flame instead of what it's supposed to cast. I also note that, in the DOS versions, transferring a monster from BT2 to BT3 (something the transfer program allows, even though the one in the C64 version does not) results in one that keeps its HP and AC, but will only cast Mage Flame.)

One other thing: What does the XP table look like in the BT3 remaster?

If I want maximum fun, which option would you recommend ? I assume reset to LVL 1 ?

Here's what I am thinking:
* The starter dungeons of BT3 can take a long time to get through with a fresh party, to the point where you might want to keep your old levels, at least with the intermediate transfer (which puts you just below the level the game expects you to reach the first dimension at).
* If you are playing with the legacy mode option that increases XP requirements, I would choose the intermediate transfer; then, when asked for the name of the Mad God, enter Chaos in order to skip the first starter dungeon entirely. (The first starter dungeon is where you find this clue, and I believe the original manual gives this bit of information in the part about transferring characters.) Then, you can breeze through the second starter dungeon (you can actually APAR down to the third level if you want), kill Brillhasti, and be on your way.
* If you are *not* playing with that legacy mode option, you can either proceed as above, or do a level 1 transfer and start over. (In this case, ignore that Chaos hint until you find it in-game or feel the first starter dungeon has gotten too boring or annoying.)

By the way:
* In classic versions of 3, if you reach level 35 naturally, the old man will actually tell you about the first dimension without having to beat the starter dungeon. Also, at least the DOS transfer program will cap your level at 35, but you keep your HP, MP, and (in the DOS version) XP.
* In the BT1 remaster, choosing the legacy XP option actually uses the XP tables from the DOS version; this means that you may want to have your spellcasters choose Conjurer or Magician (not Wizard) as their final class. Unfortunately, this isn't such a good option in BT2 because, from what I have read, only Archmages can learn the Dreamspell in the remaster (maybe the legacy XP option should have changed this to work like the DOS version?).