Welcome mate! Enjoy your stay. Let me (or really any of the vets) know if you need/want anything.
Since you're low on anti-tank (you have that vindicator, but you don't want him shooting at some tank when he can be killing marines, now do you) I'd actually take a melta on the tac. marines.
Since scouts are now dirt cheap you could get them and a meltagun and still have 3 points leftover. You could use this to switch the squad that has the cloaks (two sniper squads with +1 cover? Yes please).
I think you might have messed up points though - this should be 448... So there goes everything I just said
With that in mind I'd go for a MG/MM on the Tac. squad, maybe a ML on the Scouts? And maybe a SS on the vindicator, maybe TA or something for the Libby, the possibilities are endless. Alternatively you could go low gear high models and get another scout squad.
One thing I'm questioning is the usefulness of the razorback. I have a hard time justifying them when they're 55 points and fast (aww yeah blood angels) except with RAS who make them cheaper, of course, and when they're slow and can't really move and fire you maybe be better off with a twenty points cheaper rhino. Think about it. Is a heavy bolter that can move 6 and fire worth 20 points? Or would you rather take a MG and a ML in another squad?
How I would run it, based on this but without the razorback, is
5 sniper scouts (one is telion)
5 sniper scouts with cloaks
5 marines with a Rhino and Flamer
This gives you 5 more sniper shots, 5 more bodies, 3 less HB shots, and a more flamer (though you did have some more points to play with). Alternatively you could not give one squad of scouts cloaks, and instead get a MG for the marines and maybe a siege shield on the vindicator.
Hope I've been helpful, and have a great stay here at heresy!