This is the shorter first version, from Volume 1, part of the TG Grade grade 8 syllabus. I offer my performance, not so much as a demonstration, but as an introduction and starting point for your own interpretation.
With this piece the length of the phrases does not follow the usual pattern. Count the bars and you will see what I mean. This is instrumental music, but it needs to be treated rather like recitative. However... there is no continuo to punctuate your phrases, somehow you must do it all yourself. It is not an easy option, but it is a rewarding one.
I suggest that you mark up your copy so that you know where the 'landmarks' are. The places where you need to pause for breath, relax, speed up, play quieter and louder. I found it easier to work back from the second variation. The groups of rapid notes pointed the way more clearly than the bare essentials of the original theme. Van Eyck's audience would probably have known the tune already and been able to follow his musical thoughts in the way that afficionados track solo spots in a jazz performance. We do not have that advantage, but if you play this piece often (why not commit it to memory?) it should make more and more sense.
Opinions are divided, and discussion can get heated, on the subject of rubato and vibrato. My view is that whatever 'authentic' style may be, current performance has to appeal to the 21st. century listener. Music is a performance art and you have to engage the audience not lecture them. It is very much a matter of taste, do not go 'over the top' unless you particularly want to thrill or amaze. I suggest that you should do neither of these things with this piece (there are many van Eyck pieces where you can!). Try to convey a mood of retrained passion. Amarillis is hard to get! Be careful in your use of vibrato. I think the long final notes to phrases should be played absolutely straight.
The copy used was the latest XYZ edition (the first edition has some different notes).
If you are interested in such things, the recording was made at my 'work station' with a Sony dynamic microphone (F-99A 'One Point'). Interface to the line input of my on board sound card was via a B-Tech mic/phono preamp. Recording was done with LP Recorder, editing (and reverb.) with Nero Wave Editor and conversion to mp3 with Simple Mp3. The tracks have not been spliced. The computer is an HP Vectra business machine (900Mhz or so, Win98SE). Its a long way from rocket science.