The tank looks great. Being that you're fishing off the most stable kayak ever made---I wouldn't be too concerned about the tanks center of gravity. If a 230 lb man can stand on the thing in rough conditions (for hours on end), that little tank won't even be noticed. Well, as far as a difference in stability anyway.
Your biggest problem is going to be guys coming over assuming you have a case of ice-cold beer!
Side note: If it were me, though, the first thing I'd do is cut off that pump (save it for a back-up) and put an Attwood or similar in the scupper hole. That would eliminate any annoying-drag associated with a pump over the side. I suppose it depends on what exactly you'll be targeting and where. If you're traveling relatively short distances and say bottom fishing for Halibut, the tank's great as is. If you're traveling ten times that distance in a day (through heavy current), say targeting Yellowtail---not so much.
Maybe go ahead and enjoy the fruits of your labor for a while, hell even catch a couple fish, then set up a pump through the scupper hole. There's no drilling required; it would take you five minutes to have a far superior tank in my opinion. No drag, no catching on kelp and such. Simple as pie.
Feel free to shoot me a private message if you have any questions about the quick and easy upgrade. It would probably be easier than recreating the wheel yourself. Personally, I love the Hobie tank, but I could send you some photos of what I did (back in the day).
In my professional opinion, the only time you want more drag is on your reel when fighting Yellowtail.
