Sorry for double post. Lost internet connection and I dont see a delete button.

First, figure out what the font sales are likely to add up to over time. Then decide how much of that you are willing to give up in order to get a lump sum up front.

Should I come up with a number based on the company's size to determine how many seats the will make the font available to? Also the company's clients?

I don't think this is something that you can logically and quickly figure out.
It's the kind of business evaluation that you have to intuit by familiarity with, and study of, the market, and through experience.
It's important to have an understanding of your foundry's place in the market, and your client's.
For starters, take a look at a large number of license agreements from different foundries, to determine what sort of licence will work for you and your client. This should be determined before you quote.
Particularly, consider "Enterprise" licenses.
Other than that, I recommend you imagine what a foundry whose work you respect might charge, and double it.

You should start by coming up with a number that provides you with a living wage. What that is will depend, but typically some formula consisting of the number of hours it'll take you to do the work * your hourly rate (which is a whole other formula).

That's your baseline. At that price, you'll at least know it was worth your time. You can then raise or lower it from there based on all sorts of other criteria, but at least you'll have a benchmark.

Good advice for calculating an hourly fee to charge for work, but totally irrelevant for calculating license fees.

Perpetual Non-exclusive, and Perpetual Exclusive are two very different things.

Nick's advice on surveying the market is a good place to start.

DTF, I think your advice is off-base as well.