Max out all of your gold mines first, you can get roughly 100k gold every 24 hrs. And you're rank 10, so surely you still have a lot items to upgrade. No need to max out your factories yet, instead just leave them at level 15.
By the way, this is currently how I use my base. I have 1 factory at level 20 to get that occasional legendary. The rest are crafting the super cheap option, and every once in a while I use the level 18 factory to craft power kits when I'm running low on them. This probably isn't the best way to use the base if you wanna upgrade your items fast, but it's very cost efficient.