RE: New Patriot XL
apc11x9 is great for this engine and the Jett90. I experimented with 11x8 for test flight, which gives lower top speed but trade off of lower landing speed for first few flights until you're used to it. You want to rev this sucker at 500 below peak, which is 12,900rpm with jettstream muffler on mine. If you fly off grass, you may not get away with 12" props, unless your runway is cut short like golf course putting green!
Regarding battery, I had to put a big 1600mah one in the tail and added some tail weight. You want to balance it per instructions.
For the fuel tank, just mount it stock behind the firewall. Location there is pretty close to the CG so no big deal. Don't bother with CG tank location and have to worry about fuel pump. The OS91 does not like fuel pumps. Tried that already and did not work well.
Regarding flaps, I use half deflection (about 3/8"-1/2") for takeoff and landing. Upside to takeoff with flaps is it will shorten your roll out and get you in the air quick off that nasty grass runway. Downside is your plane will want to "jump" into the air when it reaches good airspeed, losing that scale shallow jet takeoff. Full flaps deflection makes the bird more wobbly than I thought. You may want to put flap control on the dial instead of 3 position switch to play with small deflection for take off and a bit more for landing to suit your taste. Anyway, this is a good plane to test flap management on a propject. I have not been able to do high alpha position on landing like I can with my Cermark F16.
Final comment about landing gears. Make sure you get your nosegear as long as possible to help the plane stance as flat as possible. Mine came out slightly nose down, which helps in sticking the landing, but hinders takeoff a bit.