I'm going to tease out some answers, so please bear with me 
The caveat is they were actually sold to Navient and the old loans show closed transfered. How does this effect my credi and do I have any recourse?
This is correct. The default should have been removed, the lines closed and transferred is normal (I have them, too). It's actually very good for your credit, because it pads the age. There is no recourse, but as there is no damage, you should be OK.
Most important, which should I start paying first?
That is entirely up to you. There are several pay off schemes - the "snowball" where you pay minimums to everything, and pay the smallest loans first, adding the amounts you would pay for them to the next larger one (so the payment snowballs). This has been shown to be the best for psychological reasons ("winning" by paying off loans quickly).
There is the "avalanche" method, where you pay off the ones with the highest interest first, minimizing the amount of interest you pay. < This is my preferred method, but to each his own.
Should I only pay intestest to take advantage of tax write off or should I pay smallest unsub first?
Are you in school now? Because subsidized just means that there is no interest while you're in school (though right now, I assume your loans are Federal and at 0% thanks to the Executive Orders/CARES act - please correct me if I'm wrong). As for maximizing the tax write off - you are only getting the money you pay into interest back (capped, of course), so I would disregard the "tax write off" since it's not like you're getting "extra" money back.
Also in regards to utilization, some are over the amount borrowed due to intestesr accruing in forbearance. Should I pay them all down to under 100% or should I pay smallest first?
This is up to you - utilization has a much smaller impact when it is in regards to installment lines. If we were talking about revolving credit, it would be another conversation. I would ignore the utilization, honestly, especially if you're goal is just to get out of debt.
Also, I read somewhere here that there's a secret if I pay all of the loan except for 5-10$ then the loan continues to report and is good for installment and age history. What are your thoughts? I'm so tired of being in debt and finally in a position to pay some down on a monthly basis but want to pursue the most advantageous strategy. My credit has went from 500 to 660 in last two years and the student loans and car loan are the only debt I have.
I suspect the secret is the 9% utilization "boost" you get from FICO. Please note that this boost comes from your aggregate utilization, which includes your car loan. So, yes, you could get a boost if you paid each one down to a small percentage, and if that (plus your car loan utilization) is <9%, you'd get some extra points. As an example, my student loans are at 48% utilization, but with my auto loan, I'm actually at 55% utilization. Even if I paid my SLs down to $50 (which would be .2% util there), my total loan utilization would be 29%... so I would not get that bump.
You can pay down the loans to a small amount for age, if your servicer lets you ride out the time on the loan, that's great! But not all do. I wouldn't rely on it as a tactic - I had my loans out to "next due" by 3 years, and the COVID forebearance changed all of that (I suspect that when my loans were transferred it would have knocked that back, too).
Best advice: Pay down your loans in whatever way makes the most sense to you. I am focusing on my auto loan because my student loans are at 0% right now (it goes back to that "avalanche" highest interest tactic I prefer). Some people are accelerating their student loan payments while they're at 0% so they know 100% of payment is going to principle, so when the forebearance ends they will have less due *and* less interest to pay.
Definitely keep up with the student loan payments, and keep working on your credit file. The key is patience, since so many of the factors for a good score are tied up with time, and there's not a lot you can do there. IMany banks use soft-pulls to increase their credit limits over time (and maybe you can get CLIs from the ones you hold now). Cap1 is known to "bucket", so just wait a bit, and grab some cards that are more reliable about CLIs (Citi, Discover, BofA, etc).
And just FYI: You don't need a lot of credit lines for a good score, just a long positive history. My partner had one installment (mortgage) and a single revolver and still had scores in the 800s. If you can make the cards work for you, that's awesome, but if you decide you don't want/need more cards, that's also OK. I know we're a bit credit card obsessed on this board (which makes sense), just know it's not necessary for a great score.