I think that walnut is probably the perfect wood to learn with. It mills nicely and you almost have to try to ruin it to end up with any drying defects. as with any wood you have to sticker it well and stack it flat, but walnut is generaly very well behaved and rarely warps or twists excessively. I have even had walnut that I never coated the ends have less end checking than other species that were end sealed imidiately after bucking into logs.
I tend to mill over size from what I want the boards to be. I usually mill everything at 2 1/4" which will shrink down to a fat 8/4. If you mill to 8/4 it will end up 7/4 after it is dry. I don't mill anything at 4/4, but if I did I would proably mil at 5/4 or maybe 1 1/8 if I knew I wanted 3/4 finised boards.
I usually try to capture the pith in one board knowing that I will cut it out when I end up using it. ocasionaly I will try to split it if that will net me more slabs out of the log. Trying to put the pith in one board also gets you the least and most consistant grain run out as well, which will make the boards more desireable.
Your walnut is a bit diferent that what we have on the west coast so take my coments with that in mind.