At the moment, I only have the knowledge to correctly answer question 3.
Wire wheels smooth out the metal surface, leaving the rust in the pits (not good). The smoothness is not good for paint adhesion either; the lack of tooth allows paint to flake off in sheets.
I like wire wheeling for deburring parts, and for bolts and things that will be left as bare steel. These bare steel items have to be oiled regularly to keep rust at bay.
Wire wheels seem to eject wires in use, so you have to watch for that. Some get stuck in my clothes, so I have to pick them out... Obviously, you don't want to get a wire in your eye.
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I have tried dipping steel parts in a giant tupperware full of hydrochloric acid, and it works for removing rust. It can take between minutes to hours depending on the amount of rust. You have to watch your parts carefully, as it will eat away at good metal too if you leave it in too long. Once you remove the part from the acid bath, it will rust in less than a minute, so I dipped it immediately in a sodium bicarbonate bath immediately to neutralise the acid. With the acid neutralised, you can then take your time to dry the parts.
The acid didn't change the surface finish much IIRC.
Strong steels such as 10.9 bolts are at risk of hydrogen embrittlement, so don't dip these.
The acid fumes are very strong... I remember coughing and crying because of it. I seem to remember that a full-face military gas mask with an activated carbon cartridge worked, but you still have the rest of your body that's at risk.
I stopped using hydrochloric acid for de-rusting over a decade ago; I just found it too dangerous for what it does.
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Sand blasting so far is my favorite. It's relatively easy to remove any traces of rust, and it leaves a rough surface finish that gives paint a tooth to bite into for good adhesion. No consumables; I recycle the sand (crushed glass actually), and I just buy as needed to compensate for the losses.
The rough finish is good for paint, but not good for bare steel. You should probably go over the surface with a wirewheel if you want to leave the steel bare.
This one carries the risk of silicosis if you breathe the fine sandblasting dust. I do it in a closed cabinet with a fan keeping it under negative pressure, so I don't think I breathe too much of the dust.
[This message has been edited by pmbrunelle (edited 01-05-2020).]
