In the grand scheme of things however... I wouldn't worry too much about getting an ultra rare vs a simple rare Boff. There are far more important things to look for first.

Well to be honest to me it does matter (a bit hehe), i like to RP from time to time and are having a blast getting that "iconic" crew together that seems to have stuck in my head!

Still trying to figure out if i should go for rare or better BO's and i am also wondering if rare ones and better will become available during playing the game so basically as mission rewards?

Some mission rewards. But mostly from leveling rewards. You'll get around 15 BOFFs as leveling rewards as your level up to max level. You'll get a completed mission to respong to the Personnel Officer. You'll choose between 3 different BOFFS. And they in quality as you rank up. They will be Purple BOFF when you reach Admiral.

Does that mean that all BOFF's level with the player and at some point become much better (purple quality)?

No. It simply means as you level Starfleet gives you better quality BOFF personnel choices to use - assuming you want to use them.

I often replace a White with a Purple of the same species and sex. I simply make him look like the original and give him the same name as the original - right after I delete the original.

There's an easier way to do that. While at a tailor you can save your Boff, get one of the same species and gender, go back to the tailor, click load saved costumes and presto! You have your Boff back!

Ah i see, now it's more clear to me thanks and also great tip on the tailor save thingy!