when i was in your position, i made my normal run on a day off just to check it out. same time as my commute, just to check traffic, etc..

10mi will be no problem. i ride singlespeed and fixed, got rid of my last geared bike last summer. even if you have a couple hill pulls, you'll get used to it pretty quick. same for the saddle. i run a Fizik Pave CX and there was about a week of HTFU, but it's been fine for about a year now.

i've run "street clothes" down to about 35F, just making sure to have good hand protection. anything under 50F i like to have my knees covered. biggest mistake i made those first months was overdressing. 10min into my commute and i had to stop and take off a layer. now i can "read" the temp and plan my gear, knowing that i'll only feel "chilly" for about 5min.

folding foot pump sounds heavy. i had two flats last year (one a piece of wire, the other a flint shard as my route is part trail). two CO2's and adapter takes up about the same room as a deck of cards. i carry a spare tube (and patches in case of second flat), so 5min later i was on my way. and while it seemed geeky to me at first, having a bike specific multitool (Park, Crank Bros, etc.) has been nice.

you'll love riding to work. enjoy!