rust/corrosion?

Yes and Yes

You hit the nail on the head for both, but possibly the LC with the question mark can be a side effect of a dead battery on the motherboard (pram battery it's allied). Try the double flick power on deal. Turn it on to chime turn off then turn on right away. It takes a few try's but if the hard drive is good it will boot. Also your units are reaching the age that if the capacitors haven't been replaced and you smell bad fish or see moist spots on the motherboard then it is time to have them replaced.

Yup. All it needs is a little bit of dust, some humidity or dew, and it will get like that.

Storage outside combined with cold mornings can be a killer, as can evaporative air conditioning.

As for the floppy disk with question mark, the hard drive model in your picture is very prone to a head park locking mechanism jam.

There's a nylon plastic arm that has a pivot point about it's middle. One end locks the heads in place, the other is positioned over the spinning platters. When the drive spins up, the airflow is supposed to move the end of the arm, dis-engaging the lock. With age, they get stuck.

You can get past it to get data off by giving the drive a lateral twist but you must do it before it attempts to calibrate, or it will spin down.

I'm assuming the lubricant on the shaft that the arm sits hardens, preventing the arm from moving with just the force of the airflow.

Sadly, I've not needed to work out a permanent solution, I've only manually unlocked the arm to recover customer data. Removing the arm is not advised since the heads will skate all over the platters when the platters are not spinning, causing damage.

Pics are attached.

EDIT: Of course, removing the top cover is ill-advised at the best of times, and if you attempt it, you must do it in as clean an environment as you can, and place the top cover on the drive when you can. It's possible that removing the arm and cleaning the shaft and the hole in the arm might resolve the problem without the need for any lubricant. Be very careful, if you touch or mark the patter, you can pretty much kiss the drive goodbye!

Scsi HDD

I have some small 40 meg hard drives if you want one to get it going again. Suggest a battery tho. I could probably find a set of System install disks to boot the machine and format the drive for install if you wanted.