I'm planing a road trip from Seattle, Wa to Philadelphia, PA. I plan stopping off in Cleveland, Ohio to visit some friends that live there before continuing on to Philadelphia. I'm trying to do the route from Seattle to Cleveland as fast as possible. the most direct route seems to be I-90 then either continuing on I-90 or switching to I-94 in Montana. Then following that road into the Chicago area, taking I-90/I-80 to Cleveland. After I'm done in Cleveland I'll take the Pennsylvania turnpike to Philadelphia.
I have a few questions for people that have driven these roads before and some general questions about road trips.

1) I'll be doing this trip more than likely in September There is a possibility it'll be pushed back to October though. My concern is that the weather won't be as nice in October. I'm trying to avoid driving through mountain passes with ice and snow. When does it typically become dangerous to drive up there? What is the latest you'd suggest driving this route before changing plans and doing a more southern route? I'd like to hear suggestions on a southern route as back up, trying to keep it the most direct route between the two cities but avoiding as much mountain pass driving as possible. I have done some driving in the moutons before, just never when it was snowing or as high as the Rockies. I'd also be interested in knowing what passes there are on the I-90.

2) I'm wondering how long it would take to driving the distance from Seattle to Cleveland. I'll be trying to do this in a marathon drive meaning stops only for gas/food. I will have a friend with me that could drive also.

3) I'm wondering about the gas stations a long the intestates out there, are they spaced far apart? Do they all accept credit cards/debt cards at the pumps or will I have to carry cash?

That covers about everything I'm trying to find out. I'll appreciate hearing everyones comments on this. Thanks.