I was just talking to a guy that owns a small rental company in town. He was saying how slow business has been for traditional grip equipment. Specifically, he was saying he can't rent his Fishers to save his life. Got me thinking when I saw your post so I thought I'd share some business related thoughts:
1. In NYC there are tons of established companies with well outfitted grip trucks. Competing with them will be difficult because they already have their name/image out there and they likely have way more equipment than you'll be able to get as a startup.
2. Check out what the market will bear as far as grip equipment. Are the companies in NYC so busy they can't keep up? Or is business slow? If it's busy, that might be your opportunity to cater to those who can't get equipment from the established companies because they're so busy. If they're slow, you might be getting involved in a business that doesn't have enough customers/demand.
I'd say differentiate yourself by having traditional grip equipment PLUS a whole lot of indie type equipment for the smaller guys.
That might be a great way to make a name for your company and ensure you're not relying solely on one customer base that is already being served by a large number of established companies.