I've never put on a major, so I'll defer to someone with experience in that field, but everything I've heard says that cash payments are very hard to extract from sponsors. There's a profit/loss statement for the 2016 Georgia State match in this thread, and they picked up $2000 in cash sponsorships total, against about $23,000 in stuff donations. Nationals might have more pull, but I don't think it has 30 times more pull. On the flip side, there's probably no need for a swag bag line item if we're only accounting for cash—sponsor donations will cover it.
I would call 3 ROs per stage understaffed for your average USPSA match, and 15 stages a little short for a Nationals. A stage of normal complexity probably wants a timer guy and two guys off to the sides; three per stage means nobody gets any breaks.
Don't forget that your revenue will also be reduced by up to about 3%, for match fees, if you're taking credit cards, which is increasingly expected.