In the required items list on Towerhobbies, it lists 4-40 x 1-1/4" bolt and blind nut set. In the Accessories Needed list it has Great Planes Bolt Set/Blind Nuts 4-40x1-1/4" (4) and Great Planes Bolt Set/Locknuts 4-40x1" (4). So do i need both or just the 1-1/4" Blindnut set. Also, is 4 enough of each? And finally, what are these used for (both: Blindnut and locknut?)

It's hard to tell. I'd get the 1-1/4" set and get the other set at your LHS if it turns out later that you need them. These should be for installing your engine mount or mounting the engine.

A bolt set with blind nuts is not the same thing as a bolt set with LOCK nuts. Maybe a set of each is required? You know that the blind nuts and bolts are required, so it would probably be best to get that and then purchase additional hardware through your LHS like Bruce mentioned. I can't think of any place on the plane, except maybe the engine mount, where locknuts would be used.

The 1 1/4 with blind nuts is for the engine mount to the firewall. The other four with the lock nuts are for bolting the engine to the mount

You don't need either. The 4*60 doesn't use any 4-40 hardware. Also, any bolts other than the engine to motor mount screws is supplied in the kit. The engine screws may also be included, but I always use #8-32 Socket heads and thread the mount.

By the way, I just finished building my second one and they are a great plane.

Don

It's the ARF I assume
You only need the bolts and nuts to attach the engine to the mount... Depending on what you prefer, some people don't even use this setup, but thread the mount itself and tighten the bolts to it.