I can't see much point in researching and fussing much before a money purchase. You're bound to get it sooner or later, so you may as well get it sooner, so it can start earning you money. Once you've got it, then you have any amount of time to decide where to finally put it, and how to set it up.
As for a donut purchase, then usually you either want it or you don't. If you want it, then surely you already have a vision in your head of how it will fit into your Springfield. And if you don't, but just know that you have to have it, then see above.
I have a plan for my Springfield, and I have strong opinions on where everything should be, but I still don't see much point in planning too much pre-purchase. Maybe I'd feel differently if I'd used up all the available land.
Also, it's clear that quite a few people just plonk buildings at random on grass anyway.
