As a newbie, should I spend my limited experimental time playing with different yeast combinations or play with blending grapes? Or are there other things that I could experiment with such as oak, tannin, acid, etc.?
As a 'newbie' myself, I'd suggest just making a basic drinkable wine first and getting the experience to simply produce. There's sooooo much involved and so many variables to consider in this.
More to your point, the yeast's, grapes and acids are on the front end of the process and the oak/tannins on the back end so from what little I know so far you could probably do both if so inclined. Yet you'd not have a baseline from which to work with until you get the basics down and then go from there to see the changes you've implemented.
yeast versus variety of grapes has been tabulated in many places on the internet by seasoned vintners and supply houses. I would suggest blending of various wines would be more fruitful in developing good wines.