The owners manual for your car should answer all of these questions. If you don't have the owners manual, then I'd consult HPI's website for support. I don't own an HPI product so my comments to your questions will be vague. On breaking in the engine, use the plug that comes with the engine. After the break in period, I'd ask your local hobby shop for their advice on plugs for an HPI. On fuels, again just patronize your local hobby shop and ask them for their advice. Most hobby shops carry a couple of different brands (I use Byrons 20%). A word on fuels: once you start using a certain fuel to break in an engine, I'd stick with that brand because that will make tuning easier. Thank you for your service in Afganistan. My employer is Uncle Sam as well.

Be safe
Brian