That's not rent, that's just continuing to pay the airtechs. What's the point of building a plane if you can't continue to make money off of it?
The Temple is full of mooks and no-one there is excessively hard to take down, just shoot the chaff and most of the rest will panic. Some Milkors or thrown dynamites can be painful if you're unlucky, not to mention Gillman snipers, but it's not a terribly hard mission. Indirect weaponry if your own is good for this mission since the map is relatively open but full of jungle.
One idea for avoiding an initial CF I saw is to beeline immediately for the courtyard and kill the cultists as they try to come inside, since the walls are in the way for most of their guns.
Golden Academy is one of those missions that showcase Solarius' fetish for vertical maps, just like Dioxine has a thing for underground maps.
The Stormclouds are a bit troublesome, but Syndicate HQ was worse for me.
What
do you have if you don't think you have enough firepower for these? And what's eating all your money? You can try temporarily firing some engineers/scientists, or at least supplementing your income with manufacturing. It no longer makes money overall, but it might be enough to staunch the bleeding. Maybe sell your interceptors if you're not getting a positive cash flow out of looting UFO crash sites.