Blender is a powerful program and if you don't have a fast enough rig, you won't be able to do the things you really want to.  Forget about simulations, or large scenes.  
Get 32gigs of ram or more, (ddr5 ram just dropped in price), Get a VideoCard with 12gb of vram or more, get a large M.2 drive, and an 8 to 16core Processor.