Weight of float is determined by distance you are fishing not depth. Like normal waggler fishing I prefer to go as light as possible, having said that I've found you need at least 2BB as a bulk when slider fishing.
I would probably still use a fixed float at that depth. With a 14ft rod. However, a medium size body, anntenna waggler type float would be suitable. Taking about a 2grm bulk plus droppers. Make sure the eye is small enough to stop the knot though. Some of my sliders are 12" long and take 6 or 7 grm plus brass base inserts, for waters 20 plus ft deep though. [:0][:0][:0]
Its very difficult to find slider floats with small enough eyes so I use float adaptors with swivel eyes like these http://www.ebay.co.uk/itm/25-X-QUICK-CHANGE-SILICONE-RUBBER-FLOAT-ADAPTORS-/160758829735?pt=UK_SportingGoods_FishingAcces_RL&hash=item256df912a7 I adapt them by closing the wire loop to slit by squashing with a pair of pliers.
A lake and river slider are two very different animals / techniques. I would begin on a lake, as the float is easier to control / cast. Learn how to correctly tie the slider knot. 2 knots are often required when using heavy rigs, to prevent any slippage. Look for any articles on slider float fishing by Ian Heaps, as he is a master of the technique. His slider floats are top drawer too. Good luck with it all. Once mastered it is a top method to have in your armoury. [:T]
I would only usually fish the slider in water over 12 foot deep, and start with a bulk about 4ft from the hook, with 2 or 3 droppers. I personally think 2BB isn't enough, I would use half a dozen 3AAA at least. There are all sorts of float stops, but I don't find anything easier and more reliable than a couple of stop knots with the ends left about an inch and half so they go through the rings easily. It's a long time since I fished this method, and fully intended doing so this winter at a really deep water venue near me, but I haven't got round to it yet. I reckon it's a very good alternative to the tip in deep water, especially the days when bites show hardly any movement on the tip and you are sometimes left wondering whether you should have struck. I'm a little old fashioned so forgive me if any of this has been modified by todays very good match anglers.
Yes- I have used for casting against lilly pads when there was a big tow on the water.
A normal waggler could not cast close enough (rig needs to land beyond float) and a zoomer set up with shot all around base of float could not cope with tow.
My heavy sliders all have large brass inserts with small swivels built into the base of the float. The reason for this is 1. To ensure when casting, that the float goes first, and the bulk shot droppers follow in line to reduce tangles. And 2. It reduces the need for masses of bulk shot. With a smaller float carrying less weight, or when fishing at closer range, I use unloaded sliders.
So the loaded slider is just a variation on a theme, but you still set up with bulk and droppers down below the float as per usual.[:W]
Also out of interest I use an old rod from the 70,s for my slider work with old style high bell stand off rings, which allow for easier passage of the knot/knots,this reduces line fouling or sticking against the rod, when its raining and the rod is wet. Some rings on ordinary match rods are a little small, and cause the knot to move after a few casts. My mate has a specially adapted long Salmon rod he uses and he swears by it.
Casting a slider properly is also an art, as it can be a method prone to tangles, if you are not a smooth caster. It is good practice to learn how to feather the cast, to ensure correct delivery of the bulk and droppers so they land in as straight a line as possible, and not in an uncontrolled heap which will give problems big time.[:W]