Here goes my stupid advise. Take it for what it is worth to you.

The first time I bought my bike, I took it to a park that had a flat walking/biking path. I thought I would be cool and ride up a short steep hill on grass. I ride a hybrid, not the best tires to ride on grass. I went so darn slow up that grassy hill that I eventually ended up falling off the bike. I fell on the grass, sat up, made sure I was okay, then I laid there again for a few minutes. I didn't die, I didn't get hurt. A few people noticed (which was my biggest fear) I can do this. If I fall, I fall. I still have a fear of going for a ride over my handlebars.

As far as the rest of it goes, you will get used to it. Your ass will be able to handle the seat, you will become overall more comfortable on the bike, the more you ride.. Just do it... feel funny walking your bike uphill? Drive it. Put it on the back of your car until you can make that hill.