1) How to take off this sleeved flange. I intended to heat the flange with a torch and attempt to pull it off. Is this reasonable?
No!
To remove a poured lead and oakum joint take a 3/8" drill bit and drill a few holes down past the lead and into the oakum.. Push a screwdriver under the lead ring and lever it up. Once it's free you can began to peel the lead ring out. Now pick out the oakum and you can pull the joint apart.
2) The iron drain pipe (I believe 2") is too high for my new shower and I do not want to have to deal with iron fixtures if I can help it. Can I join a new drain fixture (i.e. something from Home Depot) to the iron, and assuming that is yes, how do I cut the pipe to give me the room. Even chipping out some floor I am going to have limited access to cut a vertical pipe.
To answer that we would need to know more about the new shower.
Will this be another custom built tile shower or a manufactured base and enclosure?
the drain is very slow. I do not know whether I have some debris from demo or it dates back a while. My standard hand snake stuck on the first 90 degree. Any advice on ways to open?
What do you mean by "the first 90"? Are you talking about the bend in the trap or something on down the line? How much snake have yourun out? What size snake are you using? You have to punch through the 90 before you can began to clear the drain line. Good luck, Tom