HQ
-CCS
-Autocannon
-2x sniper rifle
-camo cloaks
I think that sniper rifles, especially in small numbers, offer dicey performance at best. Grenade launchers might offer more utility and flexibility. Ratlings might be a better way to go if you want snipers. Shaving point of the upgrades in this list might afford you a unit of them or perhaps a chimera for your command squad.
Troops
-Veteran squad 1
-plasma pistol
-3x plasma guns
-missile launcher
Plasma is safer when employed in a CCS with a medipack. Grenade launchers would save some points here and give you the choice between crack (for light vehicles MEQ) and frag grenades (for light infantry targets). You might also consider an autocannon here instead of the missile launcher. It's cheaper, and gets 2 shots and a 12" longer range. The extra point of str wont matter, as str 8 will never kill AV 14, and 7 is just as good vs everything else.
-Veteran squad 2
-plasma pistol
-3x melta guns
-demolitions
-Chimera
Solid choice, the core troop of many mech armies. Meltas shine against heavy vehicles and MC. Demolitions is expensive at this point level and as mentioned before, losing your sergeant to a plasma misfire can have bad consequences. The points spent on those upgrades might be better spent elsewhere.
Fast attack
-2x Armoured sentinels with lascannons
A decent low end fast attack choice, although autocannons may be just as good as the lascannons at this point level. I would not expect too many high AV targets at 750 points, and autocannons give you a second shot, which is nice at BS3.
Heavy support
-Leman russ battle tank
-Lascannon
-Heavy bolter sponsors
Always a nice anchor for any force, Russes are very solid. Lascannon is not a bad choice here as it's an "extra weapon". Sponsons are ok if you intend to use the tanks as a gun emplacement, but losing the sponsons will allow you to move and fire both remaining weapons. Shaving 15 points from your list somehwere would allow you to field the shorter range, and greatly feared Demolisher. Str 10 Ap 2 ordinance is truly frightening at 750. The additional pointsfrom all of the upgrade reductions might go towards that ratling sniper unit with 10 models (Or 2 units of 5).
= 750 pts