The 214B has a max gross weight of 16,000 pounds and is certified for 8,000 pounds on the hook.
As far as being the largest single engine heli in commercial operation, probably.
Don't know anything bigger (single) out there now.
The interior is not any bigger than a B205/B212, it does carry one more pax than the other two though. Instead of a forward "4 man seat" you have a "5 man seat".
JD