adding banner ad space or side ad space to basic theme?

OK, finally have time to return to my fledgling design.

I am using WordPress at home, with a mockup server on my PC.

My site will be hosted by Dreamhost, but using WordPress.

I am going to use one of the basic themes, from the WPs collection, but not decided which one yet.

How easy, or difficult, is it to add banner ad space, or side widgets for ads if they are not already in the basic theme?

Am I wasting time looking for the perfect template, with pull down menus, and ad space? Or is it easy to pick a template that has empty space in the upper right corner and down the far right column, and just put in boxes that rotating ads will work in?

I need to be able to have active ads, eventually GoogleAds or similar. But I hate annoying ads as much as anyone, so I want to put them off to the side and also have a small banner ad upper right of each page.

The site will be website with, menus, etc. and a blog in it, not a typical current events blog. So there will be lots of active subpages, and I will want ad space on each of them.

Any help will be appreciated. Thanks.