Perhaps it would be a good idea to first come up with an ultimate, 'perfect' list, then start compromising because of available models. You'll have a goal with your army that way, and those with suggestions won't have to bear in mind that quite a few things are in fact filler.
So, bearing that in mind...
- You were right about the vox network. It's the first thing I'd like to see gone. Not only will you probably not need it on 4'x4' tables with two command squads, but veteran sergeants are cheaper and all-round better if you decide you can't go without squad level leadership.
- The Command HQ is not too bad, but I'd either make it all-counter assault or all-shooting. Senior officers with power swords don't mix with heavy bolters and lasguns. In any case, I heartily recommend a company standard. Best buy for the points in my opinion.
- The infantry platoon isn't bad, but I'd put an autocannon in the one infantry squad that's currently lacking a heavy weapon.
- I'd exchange the AF squad's heavy bolter for a missile launcher, to go with the plasma gun. I absolutely despise track guards, so I'm glad you regard them only as points filler.
It's still a bit light on numbers and marine-killing ability, but that could be remedied with more missile launchers and plasma guns, preferably in more infantry squads. It's not a bad list, just less than optimal.