I feel sorry for any and all heavies.

It sounds good if you don't know how you want to run your Heavy.

Personally, I recommend putting points into the core Armour and Shield upgrades when you can, since your base HP maxes at 600 each. If you find PG and CPU an issue later on, then put points into the Electronics and Engineering skills.

Maybe go for Grenade lvl2 so you can use Flux Grenades, they make a lot of difference when you can hit a target with one of those as it strips their shields completely, so you only need to chew through their armour. Grenade lvl 2 would also give you the option of AV Grenades to take out LAVs and HAVs, and even Dropships if your throw is good enough.

What sidearm are you using? Since the HMG is short range, having a good sidearm is a must.

That depends entirely on the map, mode and who you're with\up against. Typically my kills are at least double my assists with a HMG, but I'm running mostly advanced gear and am more point-defence/living turret in my style.

I personally avoid Ambush matches and stick to Skirmish and Domination. I perform better there.

Audacious Mandate, once you have basic plate/repair I would definitely recommend maxing out your Armour and Shield skills to increase your base Armour and Shield stats. That will probably benefit you more than upgrading your weapon at this stage. Besides, you can save up some ISK while you are running cheap gear.

Anyone who has not already done so should watch this video, from this thread. It went completely against what I thought was happening, but once I saw the truth, and used that knowledge in battle, I became a lot more effective with the HMG. No longer can an Assault with an Assault Rifle expect to beat me in a 1 vs 1 unless they are strafing like crazy.

Be careful fitting multiple damage mods; every mod after the first has a stacking penalty. So two Enhanced is inferior to a single Complex.

I believe the number is 8.5%, which is still a nice enough boost, although it will take up an awful lot of CPU.

If you have that much SP, it might be worth just sitting on it for now until you have more. No point spending it on something just because you can, and end up waiting longer for something important. I know I've made that mistake before.

Crunch the numbers to decide whether going advanced over basic on your plate is better than going with a Proto damage mod. As I understand it the increase from Basic to Advanced on plate is not as dramatic as with some other modules.

I went proto with my Kinetic Catalyser and my Damage mod first, while still using a Basic armour repair, and was able to fit it on the Standard Sentinel without any Engineering or Electronics skills. But that was before the health buff of 1.5, so the repair might be higher priority now. I assume that the Kinetic Catalyser has a different PG and CPU profile than the Plates, so I am not sure if my numbers will work for you. But I would try it with an Enhanced Repair, Basic plate and a Proto Damage mod, and see if it will fit.

Skilling to the Advanced suit is very tempting, and I would do it myself if I was sure I was going to stick with the Amarr Heavy suit, but with it's bonus to feedback damage (Laser) and my love for the HMG, I suspect I will be going with one of the other racial suits when they come out. (1.8?)

That's an understatement.