I plan to play bg1 and bg2 for the first time ever. I managed to get that you can continue to play bg2 with your bg1 character. Gonna do fighter/mage. Should I dual in bg1 or play through as a figher in bg1 and dual in bg2 or what? If I dual into mage in bg1 what happens in bg2 when I import my character?

Do it in bg2 as early as possible. Level 9, is a good time to dual class. It's easy to level up to level 10 and get the old fighting abilities back. Other benefits of waiting until level 9 is that you get an extra ½ attack/round and you have exhausted the 1d10 hit point dice at that point, what determines how much hit points your character will get. A normal mage could have half the hit points of a fighter dualled to a mage at level 9.

Another thing to take into account is that if you dual in BG1 you can choose a mage specialisation as your 2nd class. However, when you import your character into BG2 this second class specialisation is not allowed -- only primary class specialisations are allowed -- and will be lost; you will (instead) be given the chance to choose a fighter kit. So, for example, your imported Fighter/Conjurer would become a (eg.) Kensai/Mage generalist, and you lose extra spell slots.

What fighter level will I reach in bg1?

Pure fighter maximum level without TotSC is 7 (89,000 XP level cap), and with TotSC is 8 (161,000 XP level cap). Whether you actually reach those levels depends on your progress in the game, and how many quests you successfully complete.

So it is indeed better to dual in bg2. I always do all quests, both main and sides ones, which is lvl8 in bg1 in that case. Then one more lvl in bg2 and I switch to mage. Generalist or specialist and which ones are good if I specializea?

As I already said, you CANNOT specialise your mage when you dual class in BG2. You may only choose a kit for your fighter, not your mage. Probably the best fighter kit for a dual fighter/mage is the Kensai, since losing the ability to wear armour is irrelevant for your mage, and the kit -2 AC and speed boosts are nice, too. There's more to it, but those are the main reasons.

Ah, ok. Thanks. Can be closed.