The Twist I built for a kit review and several other I have heard of came out tail heavy with a .46 engine, so yours will definitely be tail heavy. You will have low power to start with so you don't want to further reduce your performance by having to add a lot of weight.

I would use mini metal gear servos in the rear, something about 1 ounce, not the micros. I would put the bettery under the tank, if possible. I might look at moving the rudder servo forward and using pull-pull instead of the rear mount. Use the lightest servo arms and cut off any extra arms not used.

Mount your engine as far forward as you can get it. Use a plastic prop, APC or MA, not a light wood one. Get one of the brass heavy hubs. A .40FP is a good engine. It just doesn't have the power of a ball bearing .46 so you need to keep the weight way down to maximize your power-to-weight ratio.