Agreed with Abetillo – what you have is certainly playable to get a hang of things for some initial games, following that, this would be my critique:
Would echo the other advice and also perhaps precede that by recommending you base your army on the codex marine list – with the option to run it as salamanders – rather than just build it as dedicated salamanders. This doesn't stop you painting them as salamanders or using them that way, but you have more flexibility if you can run them as either, especially important if you have yet to fully get to grips with the rules.
I'm saying this as someone who has put a lot of effort into building a salamanders force and has used them in narrative campaigns featuring the salamanders– they mostly get played as codex marines rules wise, but that doesn't make them any less children of Vulkan in the game.
I would strongly recommend a
minimum of 2 scout formations, at the moment you have zero listed. And at 6k points maybe a 2nd land speeder. Once you get the hang of assault rules you'll find marine scouts are an amazing unit and land speeders are great for support fire and crowd control. Have enough razorbacks so you have the option to take 1 razor per scout formation where points permit. In games i've played, terminators or scouts are often the MVP – it's scouts far often than you might expect from their comparative points cost.
On the commanders note, as other has said, commander is actually the least used 'commander'. Supreme commanders and chaplains are most useful, chaplains should go in any terminator, bike, assault formations where you have the points. Librarians and regular commanders are non-essential and most lists at 3000–4000 points would have zero of either, compared to 1–2 chaplains and 0–1 sup coms. I would always take the supreme commander for new players, but marines
can work without one later if needed.
I would not take terminators in land raiders ever in smaller points games, although at 6k you could justify it on fluff. Still, it's an eye-wateringly expensive formation – at 6k you could just take a warlord titan as bts.
At 6k I would take more thunderbolts, or at least have the option to do so. Warhounds are generally best as singles, not pairs, unless you really can't spare the points. You have a lot of tacticals, while they are a very tough formation, espec with that MW FF upgrade, I would recommend swapping some for distinct devastator formations with the option for pod deployment. Devs + 1 dread in pods is a great drop formation to use to target enemy AA to open up the LZ for thawks.
Landing craft are v fun if you can find one, espec at 6k: useful to have one in the mix, but admittedly not new player friendly as a unit at all.
If you do nothing else from this post – get some scouts!
great looking thawk, old style minis look great in salamander colours, here's a couple of mine: