HI Wellzy, I've got a surf cannon as well and they are a great start for what you are after. At some point you will need to replace the guides as they are cheap and start rusting pretty quickly but they used a damn good blank for those rods considering the price, got mine for $60 also\. I'd look to go a bigger reel than the 4000 as they cop a beating with that sort of fishing, the bigger reels are just more forgiving for dealing with repeat casting, sand, etc, something like an 8000 would work better. I've found 20lb braid is perfect, casts well and enough strength for casting heavier lures. 21g lures will be a little light given you really want to get some distance on the casts, I'd be going more around the 40-60g range at least. Buy some cheapies to start and see what you are comfortable casting. Lastly, Wanda can be a tough beach, you are going to get very sore and tired with all the casts between fish, good luck though.
Rich