Racks are really the only good way to keep rats. Once you have experienced the ease of use, you will never go back to another method.

I would build one rack using medium Home Depot mixing tubs. Six levels high is a good manageable height with these.

For one snake, I would suggest that you keep two pairs of rats. I would leave the male and female together all the time. Note the date when litters are born and make it a point to pull them off the mom when they are 21 days old. This will give the female at least a week after you pull the babies to recover a little bit before the next litter is born.

You can move the babies down to the other tubs as you pull them, separating them by sex. This makes it very easy to grow them to the exact size that you need and you can pull them and freeze them at that point.

If you end up with waaaay too many rats you can try selling or trading some. This is usually pretty easy when you have maybe a dozen extra every month.

Good luck.