after i do quest Find Icas and get icas,morin,yovel quest Special Proposal disappear and i can't get Geschutz,Minen,Buchse after i do quest Special Proposal and get Geschutz,Minen,Buchse quest Find Icas disappear and i can't get icas,morin,yovel
Definitely get Geschutz,Minen,Buchse because their recruitment is necessary for some other recruits later...and they may be missable.
As for the other quests around Icas, those should reappear a little later. You may need to finish some of your other quests that you have already accepted and do a little trading/re-visiting locations to get them to show up again. You may need to talk to the characters again, even if they say the same thing, and then check with Moana again.
Except for missables, quests should reappear if you do some trading/re-visiting locations before taking new quests.
Some are wise, some are otherwise, and I have my moments.