I have a 20 long tank that had a betta in it
Ok soo i took out the betta
and i had a major power outage and now am down to
1 cory cat
4 guppies
3 phantom tetras

what other fish could i add
i want to do a mainly livebearer tank because i lovehaving baby fish
but im really interested in Line-Breeding guppies or mollies
and if i did that would i have to divide my tank and put males on
one side and females on the other side. Which i would prefer to do so that
i can choose which fish breed
i was thinking of adding

2 more female guppies
3 more male guppies
2 more corys

and when i get these fish i will get my divider
if needed and i am going to heavily plant it so the babies can survive
what plants are recomended

Corys fair much better when kept in groups, (preferably the same species) as they are a schooling fish, so yes you could add a few more . As far as guppys go the best person to help you with your question would be Kana as i know him and his daughters breed them. Think you would be better seperating the males and females like you mention.
Plants i am not so sure about but possibly something such as cabomba, java moss & java fern, am sure there are others but not sure

in my opinion and from experience of keeping quite a few corys it is best if they are kept in groups of 4 or 5 or more of the same species. they do mix well with other species of cory but seem happiest when they have atleast 3 play mates of their own kind.

i have kept and bred guppies too. they are prolific breeders so it might not be a bad idea to keep the males and females apart. a female guppy can have more than one pregnancy from just one encounter with a male.

if u put a female in with one or more males for a coupe of days and then sperate them u can almost put money on the female having atleast one or 2 batches of babies.

i have found that the guppies tend not to eat the babies if they are kept well fed. u could have problems with the tetras eating them then again maybe not. one way of having a few babies survive is to make sure there is quite a few plants etc for them to hide in.

These comments / conclusions are based on my own observations only, I'm no expert.

Line breeding Mollies has little challenge, as the hard work has already been done by the industry. The off-spring are fairly consistant, trait-wise.

Guppies, on the other hand, tend to throw up several variations at each litter. Of course the prevalence of this depends on your starting stock.

If you seriously want to produce a particular strain, you need multiple tanks. Males and females need to be segregated until almost mature, so you can see what you have. Then you place your prime candidates back into the breeding tank.

I've found that Guppies won't eat their young, if there is a range of sizes in the tank, so they're used to them, and don't mistake them for food. Guppies that are kept seperate to young, tend to gobble them up quick smart, if the chance is presented.

Thick planting is a good idea. The female will seek seclusion for birthing in any case. I'll post up my latest breeding trap, in the DIY section shortly.

Breeding for traits has it's own thrill, in addition to the regular keeping of fishes.