note that not all abilities on upgrade cards require spending focus tokens/target locks, ie a few abilities only require you to have the token but do not mention/need spending it. so read the ability carefully.
You can use any action listed on the pilot card or upgrade cards as many times as you want in a game, but only once per turn unless designated by another card (such as "Push the Limit"). You can take the Focus action every single turn if that's what you wish to do.
As stated, Focus and Evade action tokens are cleared during the End Step.