I try to let my hens do the work but when I do incubation chicks need to be kept at around 90 degrees for couple weeks and I believe when in a controlled temperature room you will have great success.
Grit is always necessary, why would you think other wise. From day one in Free range environment that is the first thing chicks eat. Best thing for them is to grow natural, watch your chicks in Free range and see how much dirt they eat. Ask any real chicken breeder if I'm wrong. There will be...
Sand is ok but also can get compacted in my opinion. My personal preference is limerock, one being it's plentiful in my area, and second it has many protein for your chicks. Drain's well and it even reduces worms because Iit has everything to kill parasite by penetration of their exoskeleton.