As for valve spring compressors this is what I use with great sucsess is.
On the inlet valve the retainer is usually a washer with a enlongated slot that is relatively easy to push down and flick off.
The exhaust valve is a bit trickier, you need to compress the spring with the valve closed while at the same time pushing the valve shut will pop the little collets out, use a magnetic screwdriver with your 4th hand to fetch them out.
As for putting them back in, compress the springs using 2 small-med sized cable ties, this makes it tons easier to reassemble, get the retainers in order while keeping a little pressure against them from coming loose with a flathead screwdriver and cut the cable ties. All going well you should be able to pul out the parts of cable tie and straighten out the springs if they have released on an angle.
There is an official gap to set the valve clearance at I have always done it to the thickness of the cardboard on a cereal box/cigarette packet/business card...
