bomber, couple of thoughts to help you get what you need. Helmets fit differently depending on the helmet manufacturer so depending on the helmet you might need different sizes. You need to look at a site that sizes helmets measure your head per their instructions and then see for instance a peltor might be a large while a bell might be a medium. You want your helmet to fit well and it's not like buying a shirt where you are a large and for most shirts a large will fit you fairly well. Helmets need to fit snugly so most people actually try on helmets even after doing the measurements I mentioned to make sure they fit. Also heads are different shapes so a large in an open face peltor might fit while a closed face might not. Also do you want open face or closed face.
Regarding wanting an intercom in the helmet, there are several different intercom manufacturers and they don't interchange so need to know what type of amplifier you have or plan to get so that your intercom in the helmet will work with your amplifier. Don't want you spending hundreds of dollars and once you get the helmets they don't fit and/or work with your amplifier.