Re: another old Noob checking in.
Fat tires are probably more comfortable, but you may run into problems with you chain, depending on your frame offset. I have a Huffy Cranbrook that came with 26 x 2.125 tires. My chain rubbed badly on my tire, to the point that the inner wall showed through. I switched to a 26 x 1.95 semi slick tire. I had some chain rub on the tire, but not as bad as with the wider tire. The real problem with the semi slick was that I laid the bike down turning into a parking lot after a rain. I then switched to a knobby 1.95 tire. No more chain rub, no more sliding in the rain. As far as whether to go 2 stroke or 4 stroke, its up to you. I personally have only had 2 stroke motors. In the small engine category, 2 stroke motors are more powerful. Here is why: 4 stroke engines fire once every other revolution, and have a separate stroke for each action in the engine cycle. 2 strokes fire every revolution, and also complete 2 actions of the engine cycle in one stroke. The 2 stroke bicycle engines also cost about a third of what the 4 stroke engines do. However, the 4 stroke engines are generally more reliable and durable. So, it all depends on what you're looking for in a ride.