1: Using H.264 (without ML or not): Recording time limit is 29:59. ML can do automated restart but you will loose some frames.
Using ML raw/mlv: No time restriction. Only card space, battery life, cam temperature limit exists.
2: H.264: See manual page 188.
MLV/RAW: Using latest experimental builds + UHS-hack you will be able to use transfer rate between 38 and 55 MByte/s. Do the math.
UHS-hack gives best results (as things are today) with Sandisk Extreme Pro 95MB/s.
BTW: Never heard of Sandisk Ultra Plus 80MB/s. I know Sandisk Ultra (different versions exist with write rates starting at about 20 MByte/s), Extreme, Extreme Plus, Extreme Pro. Label numbers are for read only, you need to know write rates. Get a decent cardreader and use some benchmark program to find out. See
www.cameramemoryspeed.com for details.
3: Answered. Consider using external power source.
4: You have to use a cardreader and your PC. Google helps.
You don't need ExFat for recordings exceeding 4 GB.
H.264 recording will be splitt into file chunks up to 4 GB, though. Doesn't matter if ExFat is used or not. And ML will not change this.
ML will be able to use file sizes above 4 GB for MLV/RAW when proper option is set and Exfat is used.