I've always done ice diving tethered, but I know some use cave techniques. Use quality gear that is serviced and tuned properly - and be sure there is no moisture in your tanks. I have always used double tanks, but that's what I dive anyway. We have used 1/3rds when diving under ice
I have mostly used Mares mr22 1st:s and Abyss 2nd:s, Both environmentally sealed and not. I have had no problems with freeflows what so ever, I used to have some trickling but after I tuned my second a bit, it stopped. My friends have used Apeks and Poseidon.
We have had max two persons in the water from one hole at a time to limit the possibility of entangling the tether-ropes. If diving under pack ice, use a sinking rope as the ice blocks are a real entanglement hazard. We have always secured the line somewhere topside, so there is no chance of it slipping in the water.
Most of the time we have had a safety diver ready topside, but sometimes not. The safety diver has double the length of the safety line than the divers in the water. If a diver looses the tether-rope, (s)he ascends under the ice asap and does not move anywhere - the safety diver is then sent in the water, and (s)he swims the length of the rope under the ice, and does a circular swim - that way the rope finds the lost diver.
Freeflows do happen, but mostly they happen top side before diving, so have some hot water with you in a thermos to melt the frozen gear. You might need the water to get out of your gear as well, and to undo clips and snaps after the dive, so have plenty.
Be careful when inflating your bc, do it with a small amount of gas at a time - if your inflator freezes, your gonna blow your corrugated hose. Some people I dive with don't use a bc under ice at all - your redundant buoyancy is the line.
Be sure you all know the rope signals you use well, and when signaling use clear and distinctive pulls on the rope.
When surfacing, swim the length of the line away from the hole, invert yourself and put your fins on the underside of the ice and tell your buddy to pull you out - that is a LOT of fun!
I wouldn't necessarily do a course. I would go ice diving with people who have done it before, and I know I can trust.
Here's a Poseidon first covered in ice. Does not affect performance.
Here is our base when we were diving in pack ice for a week
Here is our hole. Triangular is what we mostly use. Lift the blocks up rather than push them under. You have nice seats, and there is no danger of them slipping back in the hole and block it.
Here is me waiting my turn, being a safety. A full face mask is very comfortable in these conditions. Here I'm not wearing my wings, but mostly I do.
And here I am practising an emergency exit
