Guppies will likely eat all the eggs and any fry that hatch if you leave it in the main tank. Here is a basic breeding setup I posted in another thread.
The basic Cory breeding setup..
4 Basic tools needed
-scraping device and a catching utensil or if you are comfortable you can roll the egg between your fingers to pick it up. This is more difficult with species that lay large clusters of eggs.
-turkey baster to clean the container
-Over the tank specimen container. There are no openings in this container so daily cleanings are required. I have seen them for sale for $4 and $10.
1- Fill the specimen container with tank water and hang it over the inside of the tank. This way the specimen container will remain the same temperature as the tank.
2- remove eggs carefully and place them into the specimen container. The eggs will be sticky and will likely stick to your scrapper. Do one egg at a time where possible and try to scrape them to the wall of the inside of the specimen container, don't worry if the eggs fall to the bottom of the specimen container and bunch up. Viable eggs will turn a grey color in a day while unfertilized eggs will turn white. Remove these if you can, along with any eggs that have fungi growing on them.
3- Eggs will hatch 3 to 5 days after the parents spawned.
4- Start feeding around 2 days after the the babies hatch. If you see any babies without an egg sac you know it is time to start feeding. Very fine flake food will work; do this several times a day in tiny amounts.
These babies still have their egg sac
This baby is around 3 days old and does not have the egg sac.
5- Water quality is key for fry survival. Remove 50% of the water in the specimen container at least once a day. I remove the water from the specimen container with a turkey baster and pour it into the main tank. Make sure that you remove any food from the bottom. Once I remove 50%, I fill it back up from the main tank. It is best to do this an hour or two after feeding to make sure left over food doesn't pollute the water. Fry are very poor at finding food for the first few weeks so a balance between enough food for them to find it and how much they will fit inside there stomach should be considered.
6- After a few months, they should be large enough to join the main tank.