Hi there,
Well there is an app called Moises.ai where you upload your favourite tracks and it will then separate the tracks for vocals, guitar, piano,bass, drums and others into a multi track. You can then mute either tracks so that you can turn it into a drumless or bassless,etc and you can play along with it.

There's no copyright infringement as it's only for your own personal use unless you paln to upload publicly of your playing then yes, copyright infringement will happen

Generally when i play the typical matched grip, my setup is always symmetrically straight. I usually sit higher with my legs angled slightly downwards. As matched grip is kinda low position grip (around waist/belt height). Also my toms are angled just slightly towards me. This allows almost neutral position of my wrist as i move from snare to rack toms to floor toms.

For traditional grip, usually i follow the marching snare style where the snare is kinda angled more and then build the toms around that natural angled left hand going round the kit.

These guidelines which i learned from many drummers especially Dave Weckl helps me to be almost water like fluidity in motion when playing.

Well generally heel down, you would sit lower but once you start playing more intricate stuff on the bass drum, that's where heels up becomes more common. Heels down are usually more common in soft to mid level dynamics.

I'm also using playing on Yamahas too. Stage Custom (8, 10, 12, 14 and 16 toms, 14 snare and 22 bass drum, basically full size) and just a basic tom holder on the BD itself. Sometimes it may feel too far, sometimes too close, so it's more of a getting used to your own comfort zone cuz after all it's finite in distance.

Well i'm not a sifu at all, just a serious hobbyist only. There are some really amazing rock drummers out there but I'm mostly into the Jazz Fusion scene where musicality and technicality need to be extremely high.

Hit me up in the PM and we can continue there as well cuz there's a lot to it.

By means do you have like one tom, a snare , a floor tom and a bass drum? Cause that is considered 4 piece kit. Unless you have 2 rack toms instead of 1 then that is 5 piece. Mine is 7 piece, 5 toms (3 rack toms and 2 floor toms), a snare and bass drum.

Usually there are 2 ways to play todays style of jazz. Either with more swing or just typical smooth jazz straight. Can't really send a link here since i'm on post probation but will PM some stuff to you.