The only limit to how many you can transfer is filtration - if you're doubling the contents of the new tank and not moving a cycled filter over to account for this (or decreasing the amount of food your giving in the run up to the transfer) you may find yourself with an ammonia spike.
Netting and transferring will be fine assuming the stats on both tanks are similar.
well i have a total of 12 guppies, 2 fresh water crabs, 2 snails a betta and a suckerfish and the tank is brand new i have treated the water and all that but other than thats is new and unused by any fish
You can transfer all fish from old tank to new tank, but only as long as you transfer the old filter to the new tank as well, or all the old media from the old filter into the new filter.