Maxi mods would be a good idea but be careful. They're POWERFUL. Like insanely powerful. I'd suggest only modding a maxijet 900 tops for a 90g tank. I tried modding a 1200 and it was eons too powerful for my 65g.
There are LOTS of pre-made kits out there nowadays for very reasonable prices. I'd suggest buying one of those. bulkreefsupply.com has some good maximod kits, and there's plenty of others out there if you do a quick google search.
Also, do NOT build it with the propeller stop since you're using the wavemaker. Sure, sometimes it'll start backwards, but that in and of itself is not a bad thing and will randomize flow even more. When they start backwards, they just shoot water out the sides (albeit not as fast as when they start in the correct direction) but they still work. Would be neat to see how a tank behaved with that type of setup