You've got a lot of reading ahead of you. Hope you have some headache medicine ready.
You say flights, as in plural, which class of service are you planning on traveling in? International flights tend to be good use of miles but you'll still need a bunch of miles for the flights. So set your sights on a realistic expectation based on what you can accumulate.

For credit card signups you'll have to weigh what options are open to you. Depending on your credit, spending abilities and if a bonus is available to you (some are 1 time only bonuses). Also remember there are various kinds of cards. Cards that earn directly into an airline program and cards that can transfer into a program. The bonuses can be quite nice but you have to meet the spending requirements.
When flying it tends to be a good idea to concentrate your earnings into a limited amount of programs. So determine which program will fit your needs and earnings best and go from there.