I believe what HD lowes sells is not the same or of 'good enough' quality.
The acrylic[not plexi glass] sumps are made from 'cast acrylic' I believe.
I would use an aquarium from the DPG and make or buy the add ons . Silicone does not adhere to acrylic or plexi glass so you need to buy the proper adhesive if use acrylic.
I have made many sumps and they are easy..
Acrylic to acrylic is Weldon #4 or #16
Go glass and just use GE #1 silicone.
If you can cut glass just get an extra [20g for $20] tank at DPG and harvest the pieces.. That is the absolute cheapest way to build quality.