I would like to know at aproximately what level you finished the game (in normal mode) and what was your party size. (I´m using a 6 member party and would like to get an idea at what level they will finish)

I had 6 character the first time, and I finished at level 16.

I had 6 members and they finished between 16 and 18. It depends a little on class, race, who you give the tome of experience to and if any die at times along the way. I would say 16 to 17 is probably the average for a six member party.

That means that leve 30 is only attainable in solo mode? Or do you keep your xp if you continue in HOF mode?

Yes, in HOF mode you import your old characters.

you can get level 30 even with 2 characters.

No way only if you use Dalekeeper or something that ignores the exp-lvl violation.

Surely if u can get to level 16ish with 6 chars then u cud get to level 30 with 2??? if u're playin 3 chars, then you should get roughly 2x the XP for a kill than with 6, gettin u near lvl 30 and u get even more with 2 chars so u cud definatly get to lvl 30.

In HOF mode, you do NOT have to import your old characters. It is entirely possible (although) a serious challenge to start with level 1 characters and finish the game in HOF mode.

As for finishing levels, I finished the normal level difficult game with 6 characters at 17th level except for two ECL1 characters who ended at 16th.

No that's wrong!

Think about 2char party. At first you get the same exp because your party has the same averange lvl 1. But your 2 chars. raise faster and you come to goblin fortress with chars at lvl 9 where a 6person party has avg. lvl 5 (only guess don't know what lvl you are at the fortress). If your 6Person party kills an enemy there they get lets say 600exp dived through 6=100per char.
Your 2 char party gets 0exp. for the monster cause its an easy fight for you (the monsters lvl is much lower then yours). So with a 2char party you might finish normal mode with lvl 20-21 but not lvl 30!