I think the best way to make a biker army is to go basic and get as many bikers as you can. This means no command squad if you can help it. Next, I think equipping your bikers with plasma guns and a multi-melta attack bike is the wisest decision because of the range afforded and stopping power gained from this layout. It is no doubt an expensive configuration, but I believe in paying for what you get, and in this case, you're getting a lot.
As for tactics, Bikes are quite versatile. The standard operating procedure will be to hang back and shoot at whatever range you're comfortable with without being in range of getting charged (18" ~ 24"). With Plasma guns and a Multi-melta attack bike, this will be no problem. If, by chance, you are fighting an army that is inherently weak in close combat or chooses to go weak in close combat (Some dark eldar builds/IG/Tau/Some eldar builds/etc), then you can use your insanely high speed to close in and engage in close combat.
As for army-level tactics, taking advantage of your inherent mobility is key, as you must create situations of local superiority in order to systematically destroy key parts of the opposing force while exposing as little of your force as possible. This means things like isolating enemy forces via terrain, forcing enemies to close in to attack you because of LoS limitations via terrain, focusing your forces on a flank that has good cover from the other, etc. While these are things that any general must learn in order to master their army, it holds doubly true for Bike armies, for while bikes are relatively resilient when compared to other infantry, they are fragile indeed when you consider the weapons that are prevalent in 40k today.