Scott,
I had a brief look at the Kelty 5600 Redcloud Pack, and it appears to be a quality product. However, it seems to be designed more for trail hiking (not much use for ice-axe loops in Europe in May/June) and would definitely be too large for me at almost 92 liters!
The most important criteria for Backpacks is torso length. You didn't indicate whether you were fitted for this when you bought the Pack? That Pack is designed for a range of 16"-22", and you may fit that range but it's something that should be checked.
Some of the other features that I prefer are panel load (lockable zippers - not much security but it helps a bit), a detachable Daypack (works great for carry-on) and "stowable" harness system (the straps are stowed behind a zippered panel during air travel, which prevents them from being torn-off by airport conveyor systems). For Packs that don't have that feature, the airlines will often "Saran Wrap" the pack during transport.
Regarding which clothing to pack, there are suggested packing lists on this site (check the Graffiti Wall) & other web sites. I'd suggest that you pack light, especially if you're going to be using budget airlines in Europe. Trains are not a problem, but it's a good idea to have a smaller Pack as you'll be lifting it onto the overhead racks! Rick's philosophy is to "pack the same for three weeks as for three months".
"If you have your bag checked is it a huge deal?" With a 92 liter Backpack, you won't have any choice but to check it. I haven't had any problems with checked luggage (so far), but it's a good idea to pack some "emergency" supplies in your Daypack in case your main pack gets "misplaced" for a few days or longer.
Since you have a few months until your trip, you may enjoy reading Europe Through The Back Door, as it covers some of your questions. BTW, I use an Eagle Creek Backpack (2003 vintage Continental Journey).
Good luck!