Pump Capasity and over flow box size

I have a 90G FWLR tank currently running with over 100lbs live rock and about 7 fish (3 mono, 3 Chromis, coral beauty) hermit crabs and one blood red shrimp. The tank has T5 lighing and circulation pump , skimmer (HOB) and a Fluval 404 ( as the stand wont accomodate a sump). In the processes od making a new stand and get a 30G sump. I would appreciate getting a little help on the return pump size i need and the overflow box size if i am to purchase. I have also looked at DIY PVC overflow designs on youtube. Would it be better to make one of those or to purchase the real one? I am sure lot of you all would suggest to drill the tank. I wish i had thought of it be4 setting up the tank and running it over the last few years. so lets lets say thats not the rout i wana take for this tank. May be when i get the next (bigger...ha ha ha) tank i will certainly do that. I am still learning and would appreciate every input. Thanks

 

You want the return pump to run at 10 times the sump's volume at 4 to 5 foot head.

Overflow should handle at least 300goh.