the marker float is a very useful tool for mapping out your swim.. simply set you rod up to fish a running lead or feeder and instead of putting a hooklength on clip a pellet wag on.(thread a snap link on main line, followed by a bead and then attach another snap link to the end of your main line) use a heavy lead though of at least an 1oz as when you have cast out wind down and tighten to the lead. then pay off line at 1 foot intervals until the float pops up. that way you know if you have payed off 5 feet then thats how deep the swim is.
regarding the bread feeder, i like to use very dry gb. you can mix it on the bank and just add water once so once its settled you will be left with a very dry mix that hardly squeezes together. this will expode out of the feeder and some particles will rise to the top thus giving you a column of smell and feed right through the layers.
it all depends on the depth im fishing in as to where i start and every day is different so experiment but usually like to fish at about half depth in water of say 4-5 feet. in say 10feet ill start at 2 feet and work my way up. the weather will dictate where the fish want to be and usually i go by the colder it is the nearer half way to 1/3 deep they will be.