You might be doing a bit overboard with your expectations and your worries.
Daily Maintenance
If you must daily fix something on any mod/kit you buy, you've got a bad unit. But daily maintenance to me and my mod is recharging battery (ideally, but not a daily requirement since I have a PT that is my main vape and I've got a 1600 mAh battery in my mod) making sure my cartomizers are topped off and I have at least two with me when I leave the house. I also carry a spare battery even though I've yet to be gone long enough to have to change batteries.
Vaping will never be maintenance free but once you find your sweet spot you can develop a routine around your preferred vape and then will only have occasional emergencies failures or real problems.
Also I wont be recommending any particular units in this forum, you'll need to post here if you want specific reviews, recommendations, vendors, etc You could ask a moderator to move this thread there or have this one deleted so you can start another with less demanding expectations.
Protected Batteries
You should go to battery school prior to getting a mod. Good stuff to know in general even with standard sets. Care maintenance there's a lot to be aware of, but really only a few things you must have or must do to get the best performance from you unit and batt combo.
I personally would never use an unprotected battery even if unit was designed and had its own 'protection' (not sure any do, but assume it's possible since they have some kind of circuit on stock units) because of all the extra work and stuff I would need to run unprotected batteries. Technically I already have most of the required items, but would have to not only insure everything was ok for use with an unprotected battery but would have to add some 'safety' checks to my daily or weekly routine. Of course those checks are part of having a protected battery, but the protected battery is one more layer of safety if I miss damage to battery, etc.
Easy way to evaluate the mod you are looking at. Some may argue with me, but this is the easiest way for me to think about it.
1. Get one with a SEALED battery connection
If you want low maintenance make absolutely sure there is no way for juice to get from cartomizer, etc into your battery through the top. Seems to be the number one killer around here. It wont always kill a battery, but it can find a way if you arent careful and PREFORM daily maintenance to keep it clean let it dry out etc. Since you have all 510 stuff there is almost no excuse for your chosen battery to have a hole in the middle of the connector (unless you have an auto switch and with your requirements I wouldnt recommend one)
2. Insure you hit your sweet spot
In my case 5V w/3.2 ohm is heaven. So my 3.7V mod will likely have a 2.5 ohm (for longevity of batt/carto) or possibly 1.7 ohm(mathmatically same sweet spot but may have issues with LR cartomizer or have to change my battery to insure long term performance) cartomizer. First one's easy, but if you NEED a 1.7 ohm cartomizer to get to your sweet spot, then your battery has to be able to handle it. Mine is a ICR 1600 mAh batt with 1.5C rating but I have the option to get an IMR instead if I am stressing my ICR in anyway using the lower ohm. You see what I mean about battery school. Its a pain I know, but if you want to use non stock batteries with no worries, you need to wade through the battery stuff.
3. If you like the stainless monster you shouldnt have any trouble finding a mod once you decide what you want voltage/vape wise. Biggest problem with finding a mod is worrying over how it will look in public at work or to the cop sitting next to you at a red light. 8-o
Any mod you choose should either already fit the 510 or have adapters available. Find one you like, with the battery capacity you want, that can handle the carto/atty you plan on using, from a respectable vendor, and go for it. Like everything here, it's not gonna be perfect out of the box. You'll have to charge the batt, assemble it, get used to it, set it down and look at it, figure out how to carry it, etc.
4. Cases
Unless you want to pay an arm and a leg for a case custom made for your chosen mod, you should do what most seem to do. Go to the dollar store and find a camera, phone, etc case that will fit your chosen mod and the stuff you need to pack daily and you're golden.
5. Safety
Tough one cause we live in the real world and nothing is totally safe or above user error. Again you need to go to school a bit before playing with some of these toys. A little bit of knowledge will at least keep you from being HARD on your batteries/unit. And you will know what to keep an eye out for even if you only have to perform maintenance once a week. If you find a peeling battery, do you put it on the charger back in your mod or do you get a new battery. If you dont already know the answer without guessing, you need to study more before buying a mod of any kind SAFE or NOT.
Remember in your hunt you need to know a few things about each to help you decide on which one will work for you.
Voltage
mAh (not a guess at how many hours it will last)
ohm rating of cartomizer/atty needed to keep your sweet spot
Replacement Battery cost
(real battery under $10 stock battery at least $20 unless on sale)
Warranty
Replacement parts cost
(even if your unit occasionally requires replacement buttons for instance. If it's the perfect vaper for you otherwise, it's worth the effort and certainly cheaper than replacing an entire eGo battery because you had something on your finger gum up the switch on it)
