You are welcome!
I usually cut the narrow part of the bottle off and away, so the surface area is bigger, but yes, I guess you could feed the tubing through the bottle neck.
How many to feed? I don't know if you guys in the UK have that, but I use whats called turkey baster. Or a small pipette from the craft store to feed the fry. When its feeding time, take out the air stone to let the water calm down. Then put a light source (flashlight or something) at one side of the bottle - the shrimp will swim towards the source, and its easier to collect them. I usually just turn the tank light arond and sit the bottle on top of it. Shrimp swim to the bottom, and I suck them up with the pipette or turkey baster.
You can collect literally 100 or so in the pipette, or way more in a turkey baster. Some people say to squirt them out into a brine shrimp net and wash the salt off under running water, but since the salt content is hardly detectable in that bit of water in the pipette, I squirt the shrimp directly into the fry tank. Salt build up isn't really an issue, since daily water changes take out that itty bitty salt anyhow.
The shrimp last about an hour or so in the fry tank, but the fry will have them eaten long before that. For a constant supply I toss in another 1/2 tsp of eggs in the same bottle the next day after I setup the first time. And have another bottle handy to start a second batch. You can usually get 2-3 days worth of brine shrimp with one bottle, before you have to use the 2. bottle.
I feed my fry 4-5 times a day, so 2-3 days isn't really that bad. When I clean out the 1. bottle, the second one is ready to use, and shrimp have hatched in that one already.
Its a ton of work to keep the fry happy, but it comes the time when you get rewarded - when they first start to look like actual fish, or you see the first spot of coloration on them, or the first time they recognize you and start begging for food.
For mine I cleaned out the 160 gl tub outside in the sun, filled it up 1 ft with water. I let the water warm up til tomorrow, and then the first batch can go outside. They get much better color, and faster growth that way - the walls of the tub are covered with thick algae, which means less feedings for me!