Now you want Mango...what am I...diced peach?
You don't have to drain from drain plug, but you should...do this after you drain the ET...and since you're removing lower radiator hose anyway, that might be safer than draining from radiator if you're not replacing radiator...just so you don't mess with radiator drain plug.
Get a crush washer for drain plug, and be prepared for your coolant bath. If you happen to drink any coolant, drink a beer afterwards...I read here that alcohol neutralizes the poison from coolant. Cool story, huh?
The upper radiator hose is the ET hose...unless you mean the one below, which is part of the engine cooling/heating hoses...and I think you have two hoses down there...just be careful and slow in removing them, as the 0-rings aren't replaceable that I know of...though you might be able to get one. The issue with those other hoses is getting to the back side of them. One goes to a hard pipe floating by the intake mani...and it's pitb to get off...and you need to be gentle as that pipe is hard plastic...and to replace the hard pipe, you'd have to remove intake mani.
I think I'd recommend passing on these other hoses. I removed the last of these ancillary hoses just a few weeks ago...and all the hoses were fine. The issue is going to be the o-ring on them...the hoses last almost forever. (You could buy all the other hoses and replace those you can get to easily, but I'd hold on this for another time. (Maybe Mango found what aftermarket o-ring sizes fit our hoses? Someone did replace one of the o-rings I know...but not sure what hose. Take your 0-rings to truvalue and see what they can do.)
To remove mech fan, 32mm long thin open ended wrench, and either a long screwdriver or pulley holding device. Don't know where guys are getting them, but here you can find them from Bimmertools.com I know.
Leave the fan up and down...don't lie it flat. It's not hard to do, but I've never done it! Use the right tools...no sledge please until you know what's up!
Damn, I missed that Mango answered you 'in line'!
You don't 'have to' replace the temp or level sensors. Temp sensor you can just get the IAT 0-ring for (see jfoj's sig)...and the ET level sensor is in a dry place. If yours is working, it will continue to if you don't break it. You can replace them, but you could also save your $5 for when you need to replace them if you want.
HTH. (Oh, in places where I offered a different answer than Mango, you'll just have to decide for yourself who to believe! He'll be a little more conservative than me, but neither of us take medication for our OCD, so you'd be okay either way!)
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Mangofy your E46!