1. This is good enough for your purpose; 99.5% or 99% are likewise good enough. Have not tried lower grades; 70% alcohol may contain too much water.
2. I got mine from a store that caters scientific experiment equipment to schools. It is available from any chemical supply house, but probably not a small quantity.
3. In view of the hazards of the stuff, I would strongly suggest :
a) purchase and store at home only a small amount - say 0.5 liter or 16Oz
. This will suffice for a very very long time.
b) store in a well-closed bottle in a ventilated place, preferably a cabinet that does not get too warm. Ordinary house temperatures are OK.
c) the storage place should be out of the reach of children.
d) for each session of use for microscope work, pour only a small amount - say, 10-20ml or less - of the alcohol into a small flask or container, so the
main quantity stays in the closed container all the time.
e) avoid pouring or using near open fire, cooking gas flames, etc, or electric sparks.
f) use in a reasonably ventilated place - not in an all-closed space.
g) as a backup safety measure against spillage, put a glass/metal/resistant/ plastic wide flat container (tray with raised rims, a backing plate etc) directly under the alcohol bottle (the bottle stands inside the container), so if the bottle is cracked or leaking, at the worst, the liquid will be contained and not spread around.
4. The alcohol is fulluy miscible with water.