Electrical – Is Insulated Ground Wire Required

I don't know what the "Electro Metro" code is, nor do you mention your location, so keep in mind my answers are based on a US installation under the NEC.

PVC conduit is fine for the whole run, and the easiest BY FAR. You can use Schedule 40 for any and all parts, buried or exposed but not subject to damage. Areas like where it emerges from the ground outside you'd need to use Sch80. Again, 18" deep (to the top of the pipe) is fine for any residential installations. Table 300.5 is the NEC section for this.

Personally I'd go with #2AL for cost savings and 1-1/4" pipe. Since you'll have a mix of 120V and 240V loads you can run one #2, one #3 or 4 neutral, and a #6 ground. They do sell 100A MHF (mobile home feeder) cable that has this combination already grouped together. Remember, this type of wire/cable cannot be run exposed. You'd have to run the conduit completely from point to point. You could also run the conduit to a big box in the house then change over to #2SER cable, but this takes some skill and knowledge to make the change over and splice.

I'd put this on an 80 or 90A feeder breaker in the main panel.

10 AWG wire.

THWN type if in conduit.

NM type if using plastic sheathed multiconductor cable. 10 AWG is typically orange. 10/3 if it needs neutral, otherwise 10/2 and re-mark the white wire as a "hot" by wrapping it with black tape.

Many 240V heaters do not need a neutral. But if you include neutral, you may thank yourself later, because it'll give you the most versatility in terms of other things you might plug in there in the future.

You can also look at the plug for your heater and see what it requires. Even if it doesn't require a neutral, you are perfectly welcome to run a neutral, and simply cap it off in the electrical box for future use.

You must choose. You are not allowed to put 2 receptacles on a 30A supply cable in this type of installation. The NEMA 10-30 is bad news and should be avoided, anything that requires it, you should replace it with 14-30.