I typically try to get as close to the upper cabinets & hood as possible, (keeping in mind that it will be caulked so don't obsess)..1/8" gap at the bottom of the upper cabinets is perfectly fine, also fine if it's tight, also fine if it's 3/16.. anything that caulk will cover is good.
At the backsplash, same deal... usually with a backsplash, it works out that you can set a full tile and work up from there... rarely happens where it leaves an undesirable gap at the top.. lay the tiles out to work, either full tile at countertop, if you have a bad gap at the top adjust to have cuts at top and bottom that are uniform, or larger cut at bottom and acceptable cut size at top...
Then, find center on all walls, lay out tiles either grout joint on center, or half tile on center, whichever ends up on the ends with the largest cut...
This is how I do them anyway...