Well, thanx for all the advice. I checked out the communtiy created stuff, which includes awesome handouts and maps i will use. Gridding all the maps would be possible but i like the smooth look of an ungridded map. Looks more "real". Having that grid is kind of disturbing and the only thing it is useful is in combat. We thought long about using miniatures at all, but after the first encounter we decided to give it a try.
Right now i scanned some maps, marked the grid in PS and faded it a bit, so that it isn't THAT obvious. Additionally, i erased the discribing numbers from it, the party shouldn't know, in what area they're in. And finally, to make it more realistic, i will cut out the rooms and place it on the table in that moment, the room becomes visible and explorable. Some kind of analog maptool, i guess. I will give that a try and see (and report, with pics, of course!).
Thx guys!