What my end goal (tier) should be as F2P acc?

eekeeboo: As a free to play account, you should look to completing missions that provide freebies when available but having a stable variety of tanks also that will allow you to complete the various tasks in the personal missions too. Try to also complete the missions like that for the SU130 as well when possible.    Otherwise, Tier 6/7 should be where you're looking to play most frequently to increase your credit base before moving to the higher and higher tiers. Where a stable income and collection of consumables and equipment will help play tier 9 and 10 with game knowledge more profitable.