The countryside is beautiful, and the best way to experience it is via motorbike. I was nervous because I'd never ridden one, nor had I been in a place where I had to drive on the left, but Pai is a great place to practice both of those things. Some noob tips:
One person to a scooter. It's much, much harder to drive with two or more people. If you're new to scooters, don't risk it.
Get a mount for your phone, so you can use GPS. They didn't have them at the rental shops when I was there, so bring your own.
Bring eye protection. In general, it's not necessary, but if it starts raining, you'll really appreciate having it.
The rental place will ask if you know how to ride. If you say "no," they won't rent to you. If you don't want to lie, watch a video online beforehand - then at least you'll have the knowledge, if not the skill.
Be careful! As you walk around town, you'll see lots of people with scratched up arms and legs, and probably even a few people with braces/casts. Don't be one of them. It's really not that difficult to ride, you just need to be smart and cautious.
And finally a pro-tip for getting to Pai: Take a motion sickness pill before the ride up. I don't get sea-sick, I don't get sick on rides, and I haven't thrown up in over a decade. It doesn't matter how strong your stomach is, you'll feel the ride. Any pharmacy will have the pills, and they are very cheap.
Just make sure to watch out for the vans - my driver was excessively speeding, and driving well over the center line in order to make the turns. He clearly drove that route multiple times everyday, and knew it well, but I was terrified we'd hit someone or something.
I just used Wi-Fi the whole time - every shop, restaurant, etc has Wi-Fi, so I figured I'd save the money. You can download maps ahead of time, so that was never an issue.
Most people are not as cheap as I am, and do pay for a SIM card while they are there. I never heard anyone complain about it. Service is cheap, and seemed to be reliable. Even in the mountains, I never heard anyone complain about not having signal.