Struts or springs - no idea.
On the struts side, we're completing a similar job on my 16v.
The VW sourced struts are 40quid each. They are Boge pieces and can be sourced at retailers for 10quid cheaper.
I personally would do both sides. It keeps the wear balanced throughout the car. And hey, if one side went - the other side must be in a similar condition.
You may want to investigate new suspension mounts. See how much play there is in the ball race. This apparently can be an MOT failure - but you'd have to be really unlucky to get such a Nazi testing your car.
Top suspension mounts are 20quid each from VW.
I'll put my money on the wheel bearings for the rumbling noise.
Essentially, when you turn they are falling apart due to the side stresses. But thats a guess.
When sourcing the wheel bearings, make sure you get the right ones. The early 88 parts do not fit late 88 models. Been there, done that.
I would personally replace both wheel bearings. You will probably find that alot of road noise also disappears when you do the change to both.
Regards,
Tin