I would use at least two holes in case one gets clogged. If you can you could use a 55g or a 60g as your
sump to add more volume and still fit in your stand. As for the overflow boxes you can call a glass shop and have them cut out pieces for you or find someone that does acrylic. With glass you can just use aquarium silicone to glue it together, downside is theres no teeth in it. acrylic I have no idea how to work with. As for your return lines theres many options, you can come over the top with pipe or you can add another bulkhead. Hope this helps.
