Welcome!
Some advice:
When you get the bike (any bike) also get a good floor pump with a built in gauge. Riding with tires underinflated is a surefire way to get flat tires, and the more weight on the tire the more likely flats will happen.
You likely should pump the tires up to the maximum rated pressure on the side, which is not correct advice for everyone, but for 'Uber-Clydes' such as yourself it is a good idea.
Also, it is very likely you will have no problem getting on and going for a short spin, but it is best to build up saddle time and mileage over time. Your first ride might be to the end of the street or around the block, but after a couple outings you can start adding a bit of distance each time. Everyone is different so listen to your body and be sure to take rest days.
Either consult a knowledgeable friend or local bike shop on how to ensure you have your saddle height set correctly. It's a simple adjustment but getting it wrong can cause pain or repetitive use injuries to knees, which you don't want - they will result in less time spent riding in the future.