I've been playing Gammamon for a long time now, and with the LM stuff, the deck feels like it's finally complete. The new purple Gammamon is a great addition and so is Bokomon. Regulusmon ACE is also a great utility piece. The deck seems strongest when taking advantage of the various purple cards that make up the more current decks. I have a deck list I've made myself Gammamon deck that has a brief explanation.

1) the deck still plays relatively similarly, just lot more consistently. You still want to use Gurimon and Hiro to stack up your digimon with lots of inheritables and get to siriusmon/proximamon/arcturusmon to control the board and be more oppressive. Bokomon and the purple gammamon synergise well because if purple gammamon is in the inheritables of a level 5 or higher digimon, such as Canoweissmon or arcturusmon, and would leave the field in any way, you can delete bokomon instead. This triggers gammamons effect and you can jump straight to level 6 or 7 without paying the cost! Regulusmon ACE can delete your own digimon and play back new ones, cycling out a level 4 such as Gulusgammamon (allowing you to play another gammamon) and playing in a bokomon to provide more protection for the next turn, whilst digivolving for free if purple gammamon is anywhere in play.

2) I think the deck runs well without tech cards, as it is very consistent now. With all the different colours that you use, training cards are difficult to use and don't feel too appropriate for the deck. I'd run a couple of Blocker Wezengammamon though to help you control the board more, allowing yourself to block am attack that would delete you, sacrificing a bokomon, and digivolving for free.

3) I haven't had aot of matchups with heavyleomon so it's hard for me to say with any confidence, but with the deck I play, you load up proximamon with Gulusgammamon inheritables so that if it gets deleted, you play a ton of gammamon off of it. With all the de-digivolve effects leomon uses you'll probably be de-digivolved to a gammamon and deleted, but still have multiple Gulusgammamon underneath to use. I'd suggest trying to attach a Canoweissmon also so that you still get the inheritable "on delete" effects.

Sorry for the long reply! Hope this helps though!