I think he misunderstood you with the stats part.
Upgrades are limited to 255. Its a hard cap, and you can only increase upgrades via data. However, if you want to do some trigger work you could setup 2-3 upgrades ex. Upgrade 1, UpgradeX10, UpgradeX100. Then when Upgrade 1 has 100 upgrades, you add 1 to UpgradeX100 and reset Upgrade 1 to 0.
Now, if its just stats you can apply a behavior to a unit which can feed an attribute which can be unlimited.
And just FYI, Upgrades cant accept requirements. A Research ability could, but a requirement would only affect the ability being shown and/or usable.
My "infinite" upgrades are a dummy train ability which starts a trigger that applies effects via catalog including raising weapon levels. You do not notice that at all. Using a train ability might not the best choice as DrSuperEvil suggested Augment ability. I think I've tested 100k upgrades and it was fine.
Before 1.5 upgrades had an actual max working level of 107 I think despite the 255 value limit in the upgrade.