Welcome from Germany (by way of Mississippi)!!
Think you've seen most of the answers, but here's my 2.5 cents worth (inflation!)
I have an 07 Classic, rode stock for first five years and just started playing with mods this winter.
Tires (MT) will run you about $550/set every 4-8K miles so it depends on how much you ride each year and your riding style. I like the twisties, but don't do too many burnouts. Just put on the Avon front and Bridgey back and total cost was less than $500 mounted!
Heat: yes, if you use her as a commuter and you spend more time idling than riding, she can get pretty warm in the summer. But she wasn't meant to sit in traffic. Park her or ride her, but don't walk her slowly through the city.
Maintenance: She's a triumph, you won't need to work on it as much as a harley! But you can certainly change the oil, plugs, etc, on your own with no more work than any other bike.
Seat: Haven't met a stock seat on any bike that was worth the long haul. But it's a simple and relatively cheap fix. Daylong, Corbin, etc., pick your poison and stay comfy
Mileage: Before the triples/secondary removals, and open tune I was getting around 38 mpg and from what I understand many on here got much better. Now, between 32-34. But honestly, you can't ask about getting more hp and worry about losing gas mileage! The big tank is so you can ride worry free longer and not have to constantly look for a gas station. My wife's Striple gets upward of 45, but we still have to stop and fill hers up while I have another gallon and a half left!
Decent cruiser: Like I said stock, threw two fender protectors on, a set of $100 easy on/off saddlebags and my ruck sack strapped down (makes a great backrest), and rode her comfortably through 11 countries on a 28 day 4500km trip last summer. Doesn't get much more decent than that
Bottom line, hop on and ride her...you'll love her or you won't, but obviously, we're all on here because we LOVED it!!