As for resistance of a taking fish on the float it's the tiny bit above the water surface that matters not the bit under water, so as said by Billy Lane use as big a float that you need to get job done.
If the rod is swooshing you do not always need a heavier float, it is down to how you push the rod, right in the middle of your head for accuracy at distance not off the shoulder, distance the float and bulk shot is from the tip of the rod, this is the fulcrum and the timing when you release the line. Too early and the float will head skyward in a big ark and go nowhere, soo late the float will speed like a bullet for a short distance and end up way short and in a tangle. A shorter softer actioned rod will always hamper accuracy over distance. A good mid to fast action rod for distance work is required, if you are going to get any accuracy whatsoever. Pellet wagglers by their very construct have fast action blanks that do not twist under load with heavy floats and are accurate over long distances. It is all about load and unload, the rod is just a spring, overload it and it all goes to hell in a handcart, underload it and distance is compromised. Practice, practice and practice again.
There are multiple ways of casting a waggler - depends on the peg and distance fished.
Under hand, over head, side cast, gentle flick.
The there's the overhead action, some use the 'still' method, rod over shoulder, float dangling, aim ,fire - this is ok for short range but a better option is an all in one motion just like a pendulem cast as rod is then already starting to compress.
Whoosing, to heavy a rod, to heavy line, float to light, not enough line on spool, drop of float to short.
When waggler fishing always wake sure you float is big enough to cast where required. You could go twice the size required and the will be no problem. Go too light and you will over-cast (swish) to compensate.
Another tip, make sure you have at least 90% of the shotting at the base of the float. This will ease casting no end. Don't put an odd shot 'mid way' down the line. This will spoil the cast and has no real benefit.
Regarding casting there are lots of methods. All have their place. Under arm sideways cast, overhead flick or even a double overhead from the front to back and cast - for tight pegs between trees.
From my experience of beachcasting, I know that the best way to become a good caster is practice. If you can't practice on the water, then find a quiet field and try different things and see what works and what doesn't and when something works, keep doing it, until it's second nature.