Just ran some tests, some of which answered some concerns of mine, others however which left more questions.
My concern has been that the AI rarely builds ships even if the relevant scripts allow it to do so. The issue is that, for most countries (other than the US) their income will typically only permit one ship to be built (maybe 2 subs if it is lucky). I just aborted a World campaign (as the USA) after I checked Axis builds, specifically the Japanese.
They had failed to have built a SINGLE ship in 2 1/2 years-every vessel in the current build queue as of February '42 were those that the scenario maker [running Crispy's Fall Weiss where he said that he simply used the default scripts] had put in in the editor. It however had bought out most land units and air units (it had like 8 air units in China). Despite my forgetting to buy the Hornet at a critical moment, I would have easily crushed the IJN later that year with the 5 carriers I would have had (+ the Pearl Harbor BBs which were NOT bombed note), esp. since the AI had his own 5 CV's scattered in 3 different task forces.
Note I ran another Axis campaign last month where the US only started buying ships after it had bought most other units, such that by the time they started getting commissioned I as Japan had turned the Pacific into a IJN lake.
Welp, I just ran some tests. I discovered that you can switch the order of the units in the scripts w/ no ill effects, specifically putting all of the ships at the top, CV's 1st if desired. My worry is that the program reads a given script from top to bottom--but once it has spent sufficient funds on ground & air units (and tech/diplo/reinforcements), there very rarely are any left over for ships, and that's assuming it started the turn with enough to buy one in the first place. But I may be mistaken, and it instead reads them in order of their % chance of a build for a given unit, but in the tests I just ran it seems like it works from top to bottom. [hence my query directed towards the mods]
I basically cranked Japanese MPPs up to 2000, turned off all research for 1939, and saw what it built. I first did a ship-only script (all cut and pasted at the top of the script), and it bought like 6 of them, incl. a CV. I then used a script I had made with sufficient ship build %'s [bizarrely, the default one had NO ship builds pre-entry!], default unit order, and it bought a CV & a sub along with 3 ground units and 2 planes. I also tested if order seemed to matter, and in the small sample I ran it appeared to (but it takes ~10 minutes before I can reload the AI autosave and check its builds so it's a slow process).
What this means is, if you need an AI faction to build up its fleet [USA & Japan most critically], you will have to [A] put in 2 scripts [RESEARCH & PURCHASE] which are active for only a turn or two where the AI doesn't spend anything, followed by a 2nd PURCHASE script in time order where it builds nothing but ships, where you'll likely have to order the unit list by desired priority.