Well, yeah.
I don't think down-angled ftilt is of any use at all. It's too slow.
The walk to sliding dsmash is pretty good, but it should be pretty well known here though. The front of Dsmash comes out pretty fast, anyway, and walking to dsmash just gives it more range, while if spotdodged the back hit on dsmash can hit them as you move past. However it's real use is that it makes it extremely easy to catch somebody rolling, and at very low % it has a tendancy to hit them with both the front hit and the back hit for 32% damage total, 16% damage each. The reason the dsmash slides is because of luigi's low traction and because the move never "forces" a stop like a lot of other moves for both luigi and in the game.(Like releasing upsmash will stop you from sliding)
Nair to aerial firejumppunch can not be practical- not with DI and low hitstun. You can catch people with a rising nair like that(full jump or short hop) by doing it from a shield, but usually it just leads to another aerial, not a firejumppunch....