Other than carrying that big tire, Idle needs to be raised if planning to leave off the hand brake in order to keep the converter loaded, you should not have to keep pedaling the throttle to keep it lit, raise the idle till there is a slight tug on the brake handle.
By running a tach and a trans brake only you will loose reaction time consistency because your focus is on 3 things--- of coarse the tree, but now your focus on the tach bringing the rpm's to launch number which is very hard to do if you linkage/cable is not perfectly smooth in reaction so there are no hitches, but still your focus is either not enough or to much rpms instead of the tree. The third being the button on the wheel you have to think about releasing all while doing the other 2. All this can be learned, but takes time and laps.
If legal for your class there are a couple of drivers aids that can eliminate trying to visually maintain rpm's. You can run a 2-step rpm switch with a specific rpm value that when you apply the trans break you throttle down all the way and the chip maintains rpm value by interupting ignition timing, releasing the button kills the 2-step and allows the engine to rpm. The second is a auto-launch control. A pnumatic cylinder on your linkage that when you apply the transbrake you can fully depress the throttle pedal but the cyl only opens the injector to a pre-set RPM (you make the adjustment), once the button is released the cyl opens the injection all the way. by using the auto-launch you gain the consistancy of the same rpm's every time without thinking about it and your full concentration is on the tree and the release button is just a reaction because your foot already has the pedal all the way down
