Yeah, finding bib shorts that fit a 6' 4" body might be tough, but not impossible. Don't be afraid to ask the taller riders in your area what is working for them...brand-wise...size-wise. It's no guarantee their choices will work perfectly for you, but their experience and advice are a good starting point to go shopping with.
I'm 6' 1" / 160 Lbs. and it's a rare pair of bibs that have straps long enough to keep me from trying out for the Vienna Boys' Choir.
As far as inseam and leg length goes, you'll be fine. Most catalogs, websites and manufacturers' information lists the inseam length. Go with a mid-line to high-line model and at 11" inseam for a starting point you should be fine. If you have skinny legs a good gripper at the end of the leg is a big plus to keep the leg from riding up your thigh.
Chamois/pad material, thickness, position and fitting is a very personal thing. Some guys like minimal padding and some like a thicker chamois. Again, there is rarely any logic or body type that goes with a given short type, chamois style or even just the look and fit of the short. I like a thin to medium thickness chamois and prefer a longer inseam length. As far as grippers go, I can use a silicon band or a woven rubber style band, but my skinny legs prefer a 2" Lycra band with a wide silicon inner band. Dealer's choice, entirely yours to experiment with.
Some shorts I need a Medium to get a good fit and some brands I go with a large. You should check out the local shops and try on a few pairs to see what works.