Don't know what kind of "bad things" you mean... if you're gonna do fry in a
tank that large get sponge filters or some other type of low power filter. I
guess theorhetically you could do some sort of cannister type as long as the
intake was buried inside some sponge or something to reduce the force of the
water flowing into it so it wouldn't catch fry. Plenty of floating plants
and plants in general for hiding will increase your fry yield and would not
require you to move the adults out when young are present. I have a mass of
hornwort in my 10 gal. guppy tank and have lost very few fry to predation
from the 7 adult guppies or the ghost shrimp that I use as a tank maid.
Feeding them well at the time fry start appearing will also decrease
cannibalism in the adults. If I were you... I'd get about 9-10 adults to
start with that are really spectacular and let the breeding begin from
there. It won't take them quite a year and you will have so many guppies,
you'll be begging people to come and take them off your hands!