too lazy to format the text, i just answered in order
series is ~8v and parallel is ~4v, so the minimum resistance and build options are very different. the style of vape is also a lot different in general, but you can build a coil to do whatever you want when you get the hang of it. im pretty close to impartial regarding my favorite, but i lean toward series (para-series especially).
i build to amps on mechs and try to balance my coil mass for the voltage of the mod.
i havnt settled on a way to clean my mechs, i have tried everything people recommend and it all works lol i dont have a usc, but i think the only concern there is paint or whatever finish getting 'washed' off. i think i remember mike vapes or some youtuber saying it happened. cant confirm tho...
complex coils are at home on mechs, and visiting on regulated
upping complexity is the only way to get really fine control over your vape on a mech. maybe it needs 2 more plies of ribbon, or different sized frames/wrap wire/diameter etc. building for a mech will tech you everything about building that you cant get on youtube or the forums (the little details and your own preferences on how to manipulate the details into your favorite vape).
i double check every screw/leg/clamp-thing when i install, and i double check everything when i re-wick. its up to you so you have to develop habits right away, and not get over confident and get lazy once you are 'good'. so far i have never had any coil related issues/shorts or anything.
i usually install/fire/color my coils for pics on a regulated mod, and check the resistance to confirm my pre-build calculations (wire wiz). never had a situation where a build that i set up on a regulated mod had a problem on a mech. also done lots of mech only builds with no regulated mod, but im cautious and aware that im upping my chances of a problem because i have shorted coils out before on regulated mods way before i even had a mech mod of any kind. its a lot nicer to see 'coil short' on a screen in those cases, but it was still a reminder that i fucked up and would have been in trouble if i was using a mech (and stopped me from being over confident and lazy lol).
i just try to use the best batteries i can and build for their amp limits.
i build for cold resistance with ss on mechs and it seems to work very well. i only recently started using pure ss coils on a mech though, so my experience is limited.
one thing to think about with any/every mech you get, is how to disable it in the shortest time. every mod is different. some are not easy to disable in short order. i have an osmium parallel box and the spring was very very soft with about .5mm throw (didnt realize it was cooked half to death when i got it in trade. was actually my first parallel box/second mech mod) was in the car one day with it and it started firing in my lap. due to its design (separate caps for each battery that can be hard to unscrew in a panic, and it fires with either battery in single mode), i had no quick way to disable it, other than to grab the scorching hot atty and twist it off using my jacket sleeve covering my hand. compare that to the hog v3 which shoots out the batteries as soon as you touch the button on the battery door. i have had the button in mine give me some problems and if it sticks in at 8v/200+w you are fucked without a way to shut it off. thankfully that battery door is like that. every mod is different, some good, some scary in this regard. go over every mech you get and try to put some thought into the absolute fastest way to cut that circuit. if you cant find a fast (within seconds) way to do it, dont trust the mod in bad situations (driving, anywhere you cant just toss it aside and let it vent etc). i run that osmium box now with the fire button screwed on barely enough to stay put and i never leave the house with it (i also made a new spring and its fine now, but im still scared of it so i treat it this way lol).
other good habits are like
@Iliketurtles says, everything other than a normal vape is a red flag. heat, sounds, feels, misfires...all reasons to stop hitting the fire button and figure out whats going on. it doesnt take long to get the feel for it all. mech mods are usually very simple mechanisms to figure out and troubleshoot/fix.
wow that was a long one. sometimes i channel
@robot zombie because i miss seeing his extremely thorough posts. hopefully some of it helps