I also have a large case with 8 fans, they move a lot of air and so too, dust. I have a reminder in my calendar to clean the filters periodically. A piece of a nylon stocking over the front of the fans openings gives me a visual indicator as to whether or not they need earlier cleaning.
My case has 4 forward-facing removable 3-bay 5.25x5.25 slide-outs, each could hold a trio of 3.5" drives or 5.25 devices-- Even though I only have 3 hard drives and an optical installed, that's okay-- I like to spread them out (one in each bay) to reduce the concentration of heat.
Buy as much power supply and memory as you can afford. Re-running the power cables after a replacement is a huge hassle if you build for neatness (optimizing airflow). Get a PS with modular cables and use only those you need. Buy a quality energy-efficient model with a good fan(s) and keep it clear of dust. Plan for expansion and get more power than you need.
Buy memory in large modules, again planning for additions-- that way you don't have to replace smaller modules when upgrading, just add in larger ones.
Re-use old components like opticals if you can to save dollars. New modular water-cooling CPU units with rear-mounted fans provide better cooling than stock (careful of over-clocking) and the fan/radiator is easier to clean than a CPU-mounted cooler (mount outside the case).