Touring - wow, i don't know anything about tires...

So I was wanting to get some new tires. But i'm not really sure how sizing works. I've got a trek 520 with all the default stuff. It says my current tires are 700x32c. So, if I got some tires taht were 700x35 they would fit fine right? And would I need to buy a new tube for these new tires as well?

Finally, about fenders... I was looking at the SKS fenders, and how do I figure out which size fender I need?

700x35 should fit fine. As for fenders, they have widths specified on them. You are between a road and MTB size but I bet road would work best. My advice: go to a good local bike shop and get some advise to save time and money.

Get fenders which could fit up to the biggest size you would ever want. Maybe a 38? I have fenders for 38, currently have 35's on my bike, and do go as low as a 30. The bigger the mudguards (that fit), the better IMHO.

Mr Bill, get the NEXT TO LARGEST SKS fender, the P45? instead of the P50....

the biggest is meant for both 29ers and big gauge 700c tires, but are cut short and out of the 26" stock, it doesn't fit around 700c tires as elegant or as fully.

The fit under the new 520 forks can be a skosh tight for fat tires and fenders; I filed some of the steerer tube overlap back at the bottom to get a little better clearance (carefully!) and now can fit 700x38s with fenders mounted on my 520.

Same tubes will fit different tire sizes. People are often advised to get new tubes whenever they get new tires, since presumably the tubes are getting old, but it's not absolutely necessary.