I'm still subbed but already burned myself with the new expansion. I plan on getting preferred for a while.

For having 1 raid per week with guildies which unlocks I'll need?

You will need:

• 
  Account Artifact Authorization (Will allow you to wear/use purple gear, Armor, Mods, Enhancement.)
  Crew Skill Unlock (Account preferable) if you craft/scavenge
  

You might want:

• 
  Unify Colors
  Hide Head Slot
  Titles Unlock
  Server Slots (depends on how many toons you have/want to play)
  Guild Bank Access
  10 Slot Unlock for GTN (If you sell a lot of things on the GTN.)
  Inventory Unlock Account
  

Weekly Needs:

• 
  Weekly Warzone Pass (You can not do Ranked as a F2P/Pref2P.)
  Weekly Operation Pass
  Weekly Flashpoint Pass
  

Remember you will only be able to hold 350k per toon. Anything over that will go into escrow which you can purchase escrow unlocks that will give you access to your money for one time only!

I played as preferred for quite a while, but I purchased almost all if not all my unlocks (can't remember lol) from the GTN for credits when I was a sub. So definitely check your GTN for all those items. Be sure to check them often too. Sometimes they will appear fast. Asking in Gen Chat might gain you some sellers too.

to add to above. unless you are only using 4 quick bars? you are going to need quick bars unlocks.

operations pass is a must if you plan on doing ops.

flashpoint and pvp pass is only if you are running more then 3 per week. (I believe, you actualy can run flashpoints beyond the three you get, you just cannot roll on last boss loot after your 3 are done)