Ok, First off... no need to apologize. We've all been there. I hope I didnt come off as talking down to you.
So to summarize your wishes: You want a long lasting and reliable mod & tank combo that does a flavorful MTL (mouth to lung).
Let me just comment on a few things, before I give my recommendations:
-"Do pre-builds that can still be swapped out exist?" I am not enitrely sure what you are talking about,
The heating element that vaporizes the liquid inside a tank or a pod is called a coil. It can be swapped out... Either by removing the coil from the tank/pod and putting a new one in, or... if the tank/pod and coil are an integrated unit, as is the case with many vape pod devices, by replacing the whole tank/pod unit.
-Filled/empty pods: Yes correct... There are some some pod devices that use pre-filled disposable replacement pods, some that use empty ones, and some that offer both.
- Tighter draw, better flavor: No, a tight draw doesn't necessarily deliver better flavor. Excellent flavor can be had at every level of draw restriction. However, it can be said that you get way more mileage... that is capacity.... autonomy... from a MTL device. It uses way less liquid and battery than RDL/DL style to deliver excellent flavor and nicotine hit.
Tank recommendation:
Aspire Nautilus 3S: This tank is tough as nails with its metal shield guarding the glass and it provides excellent flavor and coil life. I... and many others have been using the Nautilus coils for many, many years.... it is llongest running line of coils. Comes with a strong recommendation, as I use this myself on a daily basis.
Innokin Zenith 2: Great tank with great, long lasting, tasty coils. The Z-coils are the second-longest running line of coils and I use these myeself as well.
What helps with the longlevity of both of these tanks, is that you are pretty much assured to be able to buy replacement coils for many years to come.
Mod:
-Eleaf Istick Pico Plus: Small, cheap, reliable and tough as nails. These things just go on and on...
and are powerful, pracitcal and ecomical. Again: I use this myself. Pro-tip: Get it in silver, as eventual scratches won't show up as much.
-Geekvape M100 Aegis Mini 2: Thought I better give you an option for a mod with an internal battery.... in case you don't want to deal with an external charger and special batteries. Designed to be resistant to shock, dust and water this is a tough mod that will last you a long time... until the internal battery eventually gets tired.
I don't have this one myself, as I don't like devices with internal batteries personally, but I have good experiences with another mod from the Aegis line.
However, you could just buy a whole kit from either Aspire or Innokin and be happy. They come with my recommeded tanks and get good reviews:
-Aspire Zelos 3 kit
-Innokin Coolfire Z80 Zenith 2 kit
Juice recommendation:
Since you are coming off of disposables with 50mg/ml nic salt liquids. I would either go with 30mg nic salt or 18mg/ml regular e-juice at first... a high level of nicotine. As a starting point at least... you will see, if you need to adjust up or down. Regular e-juice, also called freebase, provides a scratchy sensation at the back of your throat when vaped MTL style, which I find very pleasurable, but which you may not like coming off of disposables. Give it a shot?
And... a PG/VG (Propylene Glycol/ Vegetable Glycerin) ratio of 50/50 is best for MTL... at least for most people, as it provides a good balance of vapor and flavor.
In order to find appropriate batteries use this chart:
18650 Battery Ratings and Performance Table
and please do a little research on battery safety, there are quite a few things to be aware of using these high powered batteries, as... only carry them with you in a special battery case, charge with an external charger, never charge unattended, never use batteries with a faulty wrapper... but there is more worth knowing, so please take the time to inform yourself in case you go down the road of swappable batteries.
I hope this helps... and doesn't confuse you any further, lol. If you have any questions, please ask.