There's quite a bit of I don't understand. Here are a few questions I have lingering in my head :

1. Is the "park" a physical place where guests explore with their own two feet or is it a digital space such as that in the Matrix.
The park is a physical place. There are elevators to get you into the park.

2. If the park is indeed a physical place, why can't bullets(which are very real, evident by how they can break through wood,concrete etc) affect the guests?
It could just be VFX to keep things authentic enough for both the host and guest. Afterall, it is scifi where anything is possible including androids that become self aware.

3. Why didn't the two just decrease the overall intelligence of Maeve to a level where she simply lacks the mental capacity to be any threat to both the Felix Asian dude and his Caucasian friend?
The Maive story is abit dumb if I'm honest. and that Asian guys is by far the dumbest Asian guy ever in a TV series. They could have done exactly as you said, but they didn't just cause the Asian guy felt sorry for her. And she ends up killing real humans. Nice going Asian dude!

4. If the hosts are programmed within their core code to be unable to pose any harm to guests, then how do they constrain and hurt guests? (such as the case of Logan, where he was tortured a bit).
I think they are some leniency to torture guest. But if host get overboard, the QA will step in. Qa stepped in quite a lot through out the series.