Reddit mentions of BMW FAN CLUTCH HOLDER WRENCH SET

Not hard. I strongly recommend borrowing/buying a copy of the Bentley Workshop Manual for the E30. Head removal is 26 steps. I can't realistically copy-paste everything verbatim :)

I'm what you'd call a novice wrencher and I've done it twice. Keep your parts organised (zip lock bags are good for this), and you'll need a good set of sockets/wrenches. E-torx sockets for the head bolts (buy Genuine btw: 11121726478). Torque wrench. A good straight edge and a set of feeler gauges to check head flatness once it's removed. Be sure to clean all the head bolts holes in the block before reassembly - compressed air and rags. I opted to use a small dab of straight 30W oil under the neck of each cylinder head bolt prior to assembly (torque accuracy). New head gasket obviously - buy Genuine, Goetze or Elring. There may be a lot of "while I'm in there" opportunities - timing belt, water pump, belt tensioner, coolant hoses if they're tired. Make sure the 2 alignment dowels are installed in the block before you reinstall the head! There's a tightening sequence on the head bolts you're supposed to follow. New Genuine BMW coolant...

http://www.e30zone.net/e30zonewiki/index.php/M20

If you have all the tools and parts, and you're not trying to make a race meet, I would expect it to take a couple of days?

Edit: special tool for water pump pulley/viscous fan clutch: https://www.amazon.com/BMW-FAN-CLUTCH-HOLDER-WRENCH/dp/B003180DSC