That type of mess wouldn't come from the ocv. It doesn't spray out to cover the vc like that. That clearly looks like someone wiped oil over the VC (like with a rag after a spill). Unless the oil sheen on the vc is unrelated, the ocv weeps very slightly when it does start
Is that car one owner? I can't tell by the garbage picture, no point of reference although that does look like part of the battery in the foreground. It's possible those are studs for heatshields that attach to the fire wall, however due to the perspective it's hard to tell.
It looks like a noob spilled oil on the valve cover. You can always wash it off with a hose and some spray (or the powerwasher at a self car wash). Put a cotton rag/towel over the alternator if you do that
Nah, I like Mazda now. At the time I was n a Ford Escape 2007, which was my first car (went from a 2006 escape.) Didn't really know anything about cars and didn't do any of my own maintenance. Next car is going to be a used Mitsubishi Mirage
Yes they all use the same engine (but it also depends on year). I recommend LKQ it will tell you based on your bin what is available and compatible. Their stuff is warranted and graded. It's unlikely to get a bad part from them. You don't need to flash the ecu, unless you have one of the CD...