I´ll give you some tips because i have same background
(i´ve tried every daw i know besides Protools … that is weird cause it is standard, but i am more about composing stuff and for mixing i use reaper or mixbus, sometimes just Renoise…)
so i needed to figure out how to do some things that look easier in other program.
I´ll give you example how i make drum rolls or how i synch and slice something what i can later pitch up or down.
1: create a loop. Sync it cause then it is easier to create markers (the main pieces of loop are mainly placed on numbers that represent slice number). Create markers. You can create markers by two way, place them manually (or by alt+k) or use this great tool Simple Slice Marker Creating Script by darell.barell, where you can select just some part of sample (fe 1/8 ) and then create markers which will have same lenght (so there will be 8 markers, first on 1/8, second on 2/8 of that part etc if). it sometime works and it is nice for fast slicing of straight beat.
Then in sample editor click on create a drumkit, you can latter change keyzones of individual samples. So fe. one slice (lets say that 1/8 of beat) can be on c1 - c2 second (2/8of beat)on c2-3 etc. Then you can play these samples in one octave for each (but you are limited by tones you can use, so in my example it will be 7samples of 12pitches i think). These samples wont be synched. just that original loop will, so you dont need to care about sync button.
If you dont wanna use sample keyzones for pitching and you wanna be more flexible, or if you dont have enough space on keys for a big kit you will use comand D od U. BUT YOU CAN USE BOTH AND IT IS THE BEST LIKE IN EXAMPLE BELOW.
Btw. This is way how i create drumrolls. Slice sample, create drumkit then write a notes of it (represents different part of samples, I dont use S command here because i want hear that part when i press key and if i wanna pitch something up or down i use command (because i commonly dont pitch individual hits i dont care about keyzones very much and prefer effect command).
If you wanna change just tempo of some sample and preserve pitch, use rubberband (after you change bpm of song) or external tool. Sometimes i take some loop, use extreme settings (if i wanna some weird and very scary textures, try it) of rubberband and then slice that sample by simple slicer, write notes and experimenting with some effects. And there is where 0S command come for me, i have markers for main part of that beat or texture or whatever but i dont wanna create it on every piece of it, so 0S effect makes it possible for me. It is great because every slice has it own slice numbers for 0S effect.For me, 0S is mainly more about experimenting, “key slices” about tight drum rhytms.
For example i can write this sequence. That part after D1 can be some fast break.
C1
D1
D1 S10
F1 S30
D1 B00
E1
F1
Btw. sometimes works just this. But it is not synching. Create loop, slice it to 8 same parts. Reconstruct it with same space between every note. Samples will be cuted but with or without envelope settings it have sometimes nice result and pitch remains unaffected.
c. I dont understand that question but i suppose experimenting is best way how find out .). Btw. LPB is not so complicated. If you know fl studio, you can imagine default settings of renoise like that sequencer buttons. One bar has 16buttons (sixteen rows in renoise).
when you raise lpb to 8, imagine that fl studio has 32buttons sudennly, but lenght or speed of that bar is not influenced. It is just resolution. It is more complicated when tripplets come in [sub](when you dont use LPB12 but i dont wanna complicate things even more, so… 
/>/>/>)[/sub] cause we dont have piano roll. But thankfuly to Dblue, it is solved by this great tool.
But i am sure you can find out more about lpb on forum.
But What i am telling you it is just me, renoise is very open minded and everybody have his own tricks and manners 
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so good luck 
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