At a minimum I'd do the diff mount. You're gonna be removing it anyway to drop the springs. How old are your shocks? They'll be getting completely removed, so if they're old or worn out, now's the time to replace them.

The rest of the suspension is up to you. Unless you're really a glutton for punishment, it may be a good idea to get this job done first, then rebuild the rest of the suspension another day when it's more comfortable to work on the car. Speaking from personal experience, just the springs/pads/shocks will make a profound difference on how the car rides and drives. Dropping the springs back out to work on the suspension later on just isn't a big deal so I wouldn't be too terribly concerned about the "while I'm in there" aspect of things. Once you've done it, it'll probably take you 30-45 mins to get the springs dropped the next time.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]