The AC-09 option can, at least, be fitted without problems, though iirc the GPIB needs a different FW? Not sure on that...
If the cal is recent, it's likely still good, barring faults; I got mine (8840A, AC-09), oh, seven years ago, with cal stickers over a decade old, and it passed a cal without adjustment.
1) To me, yes. They're a good basic meter with accuracy specs more often seen in a 6.5 digit unit. It's only let down by the lack of a current range lower than 200mA.
2) Keithley 195, 197, 197A, HP 3468A, 3478A are the most obvious rivals, in that general capability/price range. Solartron 7150, if you like weird and quirky.
3) Yes, it's well regarded; I've only seen positive feedback.