Hi, welcome

You are making a wise choice by getting back into riding. Not just for your health but it is fun, I'm sure you already know!

Seats are rather specific and a matter of personal preferrence. Some people swear by a particular model, while others may swear at that same model! The easiet thing to do, most practical anyway, is go to your local bike shops and see them in person. You can usually get them to put a seat on a bike, that way you'll have a much better idea of how they feel.

As far as gears, well I don't know the setup on your bike specifically but I can give you a few pointers.

Your bike has gears in the front, where the pedals are, as well as those in the back, at the center of the back wheel. One set of shifters, usually on the left side of the bars, controls the gears in the front, while the set of shifters on the right, controls the gears in the back.

If you want the pedalling to be easy, then use the smallest gear in the front combined with the largest gear in the back. This will make the pedals turn with the least amount of effort, but, the tradeoff, is you'll go slower. If you are just getting started OR going uphill, this might be useful

On the flip side, the fastest (but hardest to pedal) combination on your bike, is the big gear in the front combined with the smallest gear in the back. That will give you the most speed, which is useful going downhill or if you are really strong.

Play with the shifters a little on the bike, somewhere safe like an empty parking lot, and you'll see quickly how the bike responds. Practice a little and you'll do fine.