Will 3 sumps work is my question? I can't build plus I've already spent the money on the tank/stand.
I don't want to sound harsh, here is the but, if you are having a hard time spending a couple extra bucks on a stand you may want to hold off on this hobby for a bit. If not you are going to rush get your water in sand rock fish... Coral if u want... Then you are going to realize that you are spending a lot of time, and going through more headaches than needed.
You are going to wish that you spent the money and didn't rush. Also this is an expensive hobby, just in normal running costs, salt, ro water, electric, fish ect. Not trying to discourage you but don't want you to regret the hobby and be able to enjoy it.
If you are not handy and are uncomfortable building a stand you can post looking for some help, this is a strong community and you will get and see help from strangers, it is amazing.
The answer to your question however is yes it would work, but leaves you open to easy disasters.