This was the effect that brought the name Aphex Systems to prominence. Their Aural Exciter was something of a cult thing back in the 1970’s.
I’ve never used one, and in fact never even seen a real one. I guess they are useful if you want that particular sound. There are many other “enhancer” effects, but the Aphex one has a distinctive colouration that may or may not be to your taste. There is some information about their current model here: http://www.aphex.com/204.htm
I don’t know this particular model, but compressor/limiters can be used pre or post recording. It can be useful to set the limiter for recording, just above the peak level of the signal that you are recording. This will do nothing! unless there is some random peak during the recording session that attempts to go above 0dB and ruin your otherwise perfect take, in which case it will limit that peak and save the day.
Note that if you use compression during the recording, if you apply too much it is near impossible to correct. Use very sparingly during recording (or not at all). You can add more compression after recording if you want.
The same goes with other effects.
I like to record “dry” (no effects, or at least very little effects) and then apply effects later. There are some exceptions to this, for example if a particular effect is intrinsic to a musicians “sound”. For example, if a guitarist achieves a unique sound using his/her amp and effects, then I will let them set up their equipment to produce that “sound”, then record it as accurately as possible. In this case, there are effects being used prior to the recording, but not as part of the recording process - I am still essentially recording dry. In this type of situation I may ask the guitarist to modify their sound slightly, but only if I know from experience that their sound is not going to translate well onto the recording (To make a recording sound like it is played in an auditorium when it is played in the studio is not necessarily just a matter of adding auditorium reverb. Many instrument will respond to the environment in which they are being played, so a guitar amp cranked up to 11 in a concert hall will not sound the same as the guitar amp set the same in the studio. Most commonly it is necessary to use less effects when recording.
There are no rules here. It depends on the sound that you want to achieve.
Lets say you have chorus effect and a reverb effect.
If you chain them “instrument > Chorus > Reverb >” then the reverb will be applied to both the instrument and to the chorus effect.
If you chain them “instrument > Reverb > Chorus >” then the reverb will be applied to the instrument, but not to the chorus effect (the chorus effect will be added to the instrument and the reverb).
These two chains will sound different - it is up to you which you want.
I tend to take an experimental approach to recording. Just because a particular effect is used on one instrument and not another does not mean that you must not use it on the other. Using effects in unusual ways can sometimes produce very interesting results. However if an effect is not used in a particular situation, it may be because using it like that sounds rubbish, but then again that is also a matter of taste. Personally I dislike the sound of “Fuzz Boxes”, but sometime that is just the effect that is wanted/required.