Render Setting Parameter interaction

I'm trying to understand the Render settings and how the parameters have an effect on the render.

Up to now I have always rendered using the default settings, while learning DAZ , and got reasonable results ("Reasonable as a definitive is a reflection on my lack of skills, 
not the software. When i've tried to experiment, I've usually gone off the rails).

Watching a tutorial video, (sorry, the vendor escapes me, it was on youtube after being sparked by one of the excellent Dreamlight lighting 
training videos, I went to research something else), I dared to change some render parameters.

All other settings, shaders, etc. remained the same. 

Iray, photoreal render.

I only changed the following parameters in the render settings and, Boom!, 
a series of really great renders, and I'm trying to figure out which settings effect what. 
I had previously tried upping the quality slider from 1-3 to see what happened and noticed no discernable difference.
(Hey, more quality should be a good thing right?)

From the default settings I changed to:

min samples: 100
max samples:7500
conversion rate 99.5%

Dome and scene
Finite sphere
draw dome off
environment (from a preset setting, Dimension theory I-Radiance Light Probe)

For a sky, I used: window>pane>environment: loaded a jpeg (light dome pro)

The render time was similar to the default settings(and less time than just turning up quality setting), but I'm sorry I didn't record 
the actual comparative stats. (If it's of any import, I have a 970 GPU). I boosted the max time to 3 hours but I've never hit that limit.

I can understand that more samples should give better results, that seems intuitive, but does min samples effect anything? 
Will the max samples just keep rendering until time runs out, or does the algorithim (step back! math term!) "know when to stop"?
My examples seems to stop at conversion limit.
Conversion rate also seems intuitive, what I wonder is, after the change, the effect was dramatic, especially in the skin,
it went from , "hmm, that's pretty good if I say so myself", to "damn, that's the last time I listen to you". (Yes I talk to myself, 
often out loud, much to the dog's consternation, no judgement please)
I mean I could see the pores, also all the excellent aberrations and imperfections put in by 
the creator of the skin materials which were absent before. 
The Shadows seemed changed (less distinction between light and dark), which to me seems counter-intuitive, but changing the light settings corrected that. 

I'm wondering how these parameters interact with each other, unfortunately the video on youtube just threw them out as "Hey, of course you knew 
these parameters are what you should have...".

Is there some type of baseline (similar to the camera settings, which, to me, respond like real world camera settings)? 
I think I understand tone mapping to a basic degree (13 for outside sunny day, 9 for a dark interior as starting points
but I need to learn camera settings in more detail, a question for another day). 
Crushing blacks and burning highlights seem to correspond to Photoshop's effects.

I understand if it's a case of trial and error, after all, I'm a pencil>ink>copic marker guy dragged kicking and screaming into 
wacom/photoshop world. 
I'm quite familiar with "slide it to each extreme and see what sticks" workflow. I guess I'm looking for a "default" like the
tone map rule of thumb.

Thank you in advance for any input.