The least expensive aluminum alloy that machines nicely is 6061 T651. With carbide tooling you can run at 1000 feet per minute or more. Coolant or lubricant is almost essential to get the best finish. You must be using a router so the least messy way would be to simply brush onto the plate either a water miscible coolant, without water, such as the Blaser stuff or Shell Dromus B which is what we use. Alternatively you can use automatic transmission fluid, strange though that may seem. keep you depth of cut shallow when you are only brushing on coolant; shallow being not more than 0.05". For tooling find a supplier of high helix two flute micrograin carbide toolbiuts, Garr is one.