Skirmish is my regular site, they ask how many you're booking in because they need to have a certain number of staff on site to cope with the number of players, it's just to give them an idea of what the turnout is going to be before the day so they can properly staff it, it's not geared towards groups at all, they just won't have thought about the presentation of the site that much when they were wording the booking form. It's nothing to get wrapped up in.
Their website can be confusing and leads a lot of people to think there are a lot of Skirmish Airsoft sites around the Sheffield to Nottingham area, really there's only 1, and the best way to describe where it is would be to say it's between Worksop and Mansfield, get yourself booked in and head down there for a day, the staff are excellent guys + Paige behind the counter
They hire kit out to those who need it, they have an on site shop, the whole site's a blast and the banter with the rest of the guys is as much a part of the day as the shooting is. It's the first site I ever played at and I've kept it as my regular since then, it's just that good.
Not to turn this into a shameless plug, but if you check out the Skirmish Airsoft playlist on my YouTube channel then you'll get a good idea of what the game areas are like, plus if you have no one else to go down there with, then you can always get to know us on the forums who go there. Me, Ian_Gere, Kaza66, Gecko, BottledTorment, Chippins and a few others are occasionally down there.
Going alone really isn't an issue though. You'll make friends out of someone there on the first day, guaranteed. Probably one of the marshals at least!