miles on clock, condition, service history??? Photos may help as ultimately it comes down to what someone is willing to pay for it on the day or how long you are willing to wait for the right person
Wotcha and welcome - that model and colour was one if the first I test drove prior to making my first purchase, nice amount of grunt but nicely understated. Feel free to get stuck in post photos etc all friendly on here 😊
could be the flywheel or the clutch plate itself.
CV joints are easy to check - full lock in a car park and drive in a slow circle back and forth listen for clunking however if it were joints there would be a constant cyclic noise that changed in relation to speed
Looks to me like the connection is not fitted as flush to the plug and has rusted over time - might be arcing or just moisture, either way not a fun job to have a go at, good luck with it, stacks of Plus Gas if possible
https://www.ebay.co.uk/itm/SUBARU-IMPREZA-CLASSIC-WRX-STI-RA-JDM-EJ20-E3-RB5-ECU-GC8-GF8-22611AE800-92-00/303136451357?fits=Car+Make%3ASubaru|Model%3AImpreza|Cars+Type%3A1.6|Cars+Year%3A1999&hash=item4694572b1d:g:4QQAAOSwB4BaMCho
does this help?
The powerflow franchise may be able to help you out
https://www.powerflowexhausts.co.uk/powerflow-carlisle
https://www.powerflowexhausts.co.uk/Powerflow-Morecambe
Exhaust Craft in Whitehaven has mixed reviews
A slightly belated Wotcha and welcome - as you have seen already plenty of Fozzie experience on here so feel free to set up a build thread and keep a track of your progress 👍