HUD - depends on your likings. Ussually PokerTracker(currently ver.4) or HuldemManger(currently ver.2) is used. Now there is 1 more that is "emerging" - Jivaro, it looks better than first 2 but, has less stats that you might need in a cash game, but for MTT it's well. The only problem is it has no Trial I thinkбнщг might google and check I remebmer they were closing "basic" plan but maybe they have some sort of trial. And trials are, well trials =)
Other soft is... whele there is alot ICMizer,Flopzilla,Equilab,PokerStove... some of them are simmilar, som diffrenet or are used for different things.
For exmp. a lot of Sng players use ICMizer, but it's almost useless in cash(maybe to train All in %), and Flopzilla is good for cash.
I use PT4,Flopzilla,Equilab
There is also soft like tiltbreaker that can help you not lose you $$$ while playing
BR - ussualy the rule of 40 buyins per limit is good for cash, and 100 buyins for MTT, it is tight but will get you throuhg the varience.
This is a good cash mangment strategy