How many pairs per tank?

I will hopefully be getting a 6 foot tank in the near future...and i hope to use my old tank for breeding BN's, it is 180 litres, would i be able to breed the BN's in the 6 foot tank and use the 180 litre as a grow out tank?

If i use the 180 litre tank as a grow out tank and i moved the dad, cave and eggs into it, how would i do it, i don't have a clue how to move dad, cave and eggs without the male BN noticing it very much so as to not stress him out.

If dad kicked out eggs or some of the fry escaped, would a seive placed in front of the filter outlet be a sufficient fry saver?
Any help appreciated
Thanks

James