Where will using the boat? That'll affect what sort of effort is necessary
to arrange a slip. Some places have plenty, some places are considerably
more expensive. It varies quite a lot.

If you're going to buy a used boat be ready for lots of sudden expenses.
But as long as it's surveyed PROPERLY before the purchase it shouldn't be
too problematic. Run away from fixer-uppers as you'll spend more than
you'll ever get back out of it.

The safety class is an excellent idea. Get your spouse/partner/whatever to
go along with you. It helps when more than one person onboard knows some of
the basics. Also consider joining a local USPS chapter, if just to talk to
the fellow members about what local boating entails.

We are not new to boating by any means but we are newbies when it
comes to cruisers.
We are not looking to buy for about 3 years, I am currently doing my
homework.
We are interested in a 30' to 34' Hardtop.
Our budget will allow for a late 1980's or older.
I like the layout of the old Trojans and Catalina's.
When do we start looking for a slip seriously.
Do we get on a waiting list before we buy a boat?
Don't really want to buy a boat then not be able to use it.
I do plan on a USCG or Power Squadron Course before buying.