The easiest way to secure finances without resorting to the console is to savescum villages. For some reason, most village capture events don't actually count the village towards the number of villages you have under your thumb or get money from; only the generic village capture (where you specify how many of your forces you'll use to subdue the village), the nobleman bribery event (where he offers you the two girls), and the coven event (when Rowan stumbles on some women trying to practice "the old ways") seem to add to your weekly funds. If you use these specific events to capture all the villages pretty early on (only the generic capture one is repeatable), money isn't much of an issue, especially since many of the buildings don't really seem to do anything yet. It also helps if you can get the two ruler events that give you 100 gold each early on—the one where an orc comes to ask you how to distribute some uncovered wealth (put it in the treasury), and the one where Skordred and Cliohna are fighting (side with Skordred)—, you should have more than enough to work with. If for some reason you really need the extra income after capturing the keep, Alexia can get you another 10 gold or so per week in the tavern job.
I find the only things worth spending money on are the event-required buildings (brothel, tavern, forge, dark sanctum, arena, breeding pit); and it only really seems to be worth upgrading the library and dark sanctum, as those both contribute to your research speed, and the dark sanctum also multiplies your orcs' military strength (aside from adding to military strength, as well). You can upgrade the orc barracks, but I don't feel like that's necessary with fully equipped orc forces plus a filled out dark sanctum. I've got a military strength of 675 with 30 equipped orcs and 10 cubi, and I'm not really sure how many driders, and this is at week 32 without going through the orciad yet, and that's way more than you need for anything in the game so far. You can also save the breeding pit and arena till after you capture the keep, as well as the brothel if you don't want to infiltrate, or the tavern if you don't care about Greyhide's scenes or you're keeping yourself pure.