This is specifically addressed in the film's official novelisation. Brand was planning to land on the remaining planet (Edmund's World) with Coop and between them they would incubate ten-ish embryos using an artificial womb. These children would then form the backbone of a new human population using a mixture of surrogacy and normal pregnancy.
Ultimately, the only difference between what was planned from the start and the ultimate outcome was that instead of being managed by four adults, they started the bomb with a single adult:
This is one way. Plan B — a population bomb. Almost five thousand
fertilized eggs, preserved in containers weighing in at under nine
hundred kilos.” Five thousand children, he thought. Five thousand, in
this little vault, waiting to be brought into the world.
“How could you raise them?” Cooper asked.
“With equipment on board, we incubate the first ten,” Brand replied,
as if she was talking about planting corn. “After that, with
surrogacy, the growth becomes exponential. Within thirty years, we
might have a colony of hundreds. The real difficulty of colonization
is genetic diversity.” She pointed to the glass vials enclosed by the
device. “This takes care of that.”
She had been trying to stay occupied with the particulars of her
duties—primarily making certain that they could still implement plan
B. The population bomb had been roughed up enough that she’d needed to
overhaul the cryonics, which she had managed to accomplish with a
little help from Case. It was a makeshift fix that required
cannibalizing Romilly’s cryo-bed, but then again, he wasn’t going to
need it. Once they made planetfall, she could use some parts of the
Endurance they still needed to rig a more reliable system. They
couldn’t thaw all of the embryos at once—the bomb would need to
continue working for decades, at least.
She wondered how many children she and Cooper would be able to manage,
now that it was just the two of them. Five? Ten?
At least he had some experience along those lines.
You want a big family, Coop? It was going to be an odd conversation to
have. Probably a painful one, too—at least for him.