always defrost in tank water. Best to chop block with sharp knife into halves or thirds. Have a special container for feeding, get some tank water, thaw the block and then use dropper or spoon to put into tank. Mine usually have 3 bloodworm, I have been naughty and feeding every day except Sundays but plan to cut back as mine are right piggies.
Pond snails should be fine, general rule of thumb size of their eye to crunch apparently, otherwise if too big will suck them out or nip at them in bits and pieces.
Snails you wouldn't need to feed everyday, maybe twice a week, I have not had a constant supply for mine only rare occasions and they have been fine, changing that now as have snail critter keeper tank.
A blister pack of bloodworm will last you a looonnnggg time. Maybe to start feed every other day, you will soon learn they are quite the artists of begging, can't watch mine anymore without the begging!
p.s. definately defrost, read somewhere it is bad to drop in a cube and to thaw in their bellies..
Also if you get picky eater, they can't resist live bloodworm or blackworm.
live bloodworm packs 99p, blister packs £2.50ish to give idea ( I have a...think its a 12 blister pack and not even a third of the way through and have had 3 months with 4 puffs!) They do not starve and are on the podgy side.
Lastly lastly, from what I have read (please correct me experts please as still fairly new) DPs don't grow as fast as the others such as F8s and SAPs if concerned about their beaks.