First question: Are you printing this negative for fun, or for profit?
It sounds like what you have in mind is the use of a "film recorder". Some of these machines are capable of imaging up to 8x10 film. If it's a "16K" film recorder (a 4x5 is about 16000 x 12000 pixels), you could easily image 1200-1600 DPI of true resolution onto the film, which would probably be good up to about 3x enlargement, possibly 4x, if the original is lower contrast and doesn't have a lot of fine detail.
But there are a couple of other options you may want to consider.
If you have or have access to a decent quality inkjet printer, you may want to look into making a "digital negative" in which a negative is printed onto inkjet transparency media, and then contact printed with the paper of your choice. The learning curve might be a bit steep for just a one-off negative, though.
There's also an occasional user on this forum, Bob Carnie, who runs a photo lab up in Toronto, who is capable of imaging onto wide rolls of silver film (up to 24" or something like that) using a lightjet or a lambda for contact printing, or directly onto B&W paper.
That's probably enough to get you started...feel free to follow up here if you have more questions.
--Greg
