Is there any rule that keeps us from buying a 3-year software license? It'll cost $5000, should I send in a request first?

There is no specific federal rule regarding software.

There are rules about necessary and reasonable, exclusivity (be made only available to WorkFirst if paid 100% from WorkFirst)and demonstrate that it’s addition would support expanding capacity.

Of course, all “other” appropriate fiscal rules apply.

And Yes, you should submit an request in advance of the software purchase.