Manufactured sumps are a lot more expensive, but you can buy one if you don't want to take the time to research some basic DIY sump. Time is money
I have no recommendation for a manufactured sump, so you might have to do some online googling or wait for someone to reply to this post. Most people buy a skimmer first, then build the sump around the skimmer. If you buy a sump, then you will have to find a skimmer that fits your sump.
As for design, you can split into the common 3 chambers with baffles in between each chamber. First chamber is the drain line, second can be for whatever you want, and third chamber is return pump. The third chamber is where you will see the evaporation, so the water line will drop and you will have to top off manually or buy an auto top off. I prefer to place my skimmer in first chamber. Baffles are to help bubbles from drain line and skimmer dissipate before reaching the return pump.
Plumbing can be very basic as well. Use PVC
pips to connect to your fitting. For your small tank, I'd think the return line to be 0.5" and drain line to be 1-1.5".
Post for clarifications or questions.