Welcome to FlyerTalk!

Since it never costs anything to open a frequent flier account, you should have one even if you only rarely utilize the services. There are some (free) sites that can help you track your mileage/expiration dates (such as Award Wallet).

There is no ideal FF program. Each has its pros and cons. For example, Delta miles don't expire, and you can earn them easily, but they can be *very* challenging to use. Avios also don't expire, but redemptions are distance based, and BA charges very high fuel surcharges to fly on their metal. UA allows one-way awards and tends to have good availability, but a lot of people complain about their service.

As for credit cards, I used to want to keep the cold cash, but have found much better value in biz redemptions on long-haul flights. However these considerations will vary based on your own preferences and ability to travel.

Good luck with your new avocation!