If you call the Marinoni shop, you'll probably find someone very useful to explain to you what the different combinations can be on a Tourismo. They have GREAT customer service.

If you want to do mainly hills and steep hills in particular, I'd recommend getting a triple chainring in the front (like 52-40-30) and a cassette with a 25 in the back. Or a compact double (50-35) and a cassette with a 27 or maybe even more in the back. What will affect your performance on the hills is mostly the range of gears available to you, although the reliability of your shifting devices will also matter: if it's a struggle every time you want to change gears, you'll often loose momentum and, if you're like me, get frustrated.

As DebW pointed out, it's easier to mix and match within a company's offering (Campagnolo or Shimano) but some other matches can be made. It's usually hard or ineffective to skip three steps (e.g. put Tiagra 7-speed shifters with Ultegra 10-speed cassette!) or more, but a lot of bikes have mixed 105 and Ultegra or Ultegra and Durace components. You can save a bit by choosing some components which you consider less critical (dunno, the cassette for example) from a lower ranger and more critical parts (rear derailleur?) in a higher range. Shifters are important but really terribly expensive.

As I pointed out in a different thread, Marinoni will basically prepare whichever bike you want for you based on your measurements and needs and tastes (paint job, especially if you don't trust Mrs. Marinoni's tastes, which I have found at times dubious), for a relatively tiny fee ($100 I think). Every bike shop that sells Marinoni probably has access to this service. Otherwise you can always call them directly and see if you can get that. Or you can go directly to their shop in Montreal and have a great time!!! (And ride back to Seattle to save on gas?)

/End of Marinoni envy.