Nassarius snails breeding like mad

Hello

Two weeks ago i purchased 12 Nassarius snails from my LFS. 3 days ago i
noticed a few things on my front glass, using a magnifying glass i can now
see that they are egg sack things. Theres approx 15 yellow eggs in a clear
'bag' i suppose thats stuck to the glass.

I know that the Nassarius snails are laying them because ive witnessed it,
they climb to the top of the tank and then go off in arandom direction laying
these 'bags' every 2-5mm as they travel. The strings are about 20 'bags' long

On watching this, quite quickly they sort of grow in the bag and then hatch
in to tiny what i can only describe as mini amphipods and scuttle about.

Ive noticed two mini versions of a conical shell shaped snail on the glass
that are 1mm long and so i can only assume that there reproducing.

The reason im posting this is that i have a few questions.

1) what do they feed on as larvae

2) if this carrys on i already have over 100 egg 'bags' on the glass and
there still laying, theres one doing it right now... im going to end up with
500 snails in my tank... what do i do about that

3) has anyone else had this happen to them. My turbo snails seem to do a
similar thing. Theres a whole load of 5mm long turbos in there aswell and one
has grown to 10mm in width over the last 2 years

Anyway, wanted to share that, any comments would be good

Thanks

Warren