Selecting folders for synchronization via IMAP and other questions

is there somewhere to set which folders I want to synchronize via IMAP?

See @Gary post on the following thread on how you can do that.

And how to change the default folder for delivered mail?

You could setup a rule via “Menu / Rules” (PC) or “Tools / Rules” (Mac) to move whatever specific inbox mail to whatever mail acct folder or local folder you want.