We are traveling into Zurich the first week of April. Normally I plan my whole route and pre-book the hotels. Not knowing exactly where we want to go, is it a bad idea to leave some nights open and plan on the fly? Or is this a busy time of year for accommodations?? Train travel- does that need to be planned in advance. Also looking for "alternative" beautiful swiss and Austrian cities. (for example- don't go to Interlaken, because X town is just as beautiful and not as touristed)

Thanks!