Erin -
First of all, congratulations on your quitting the analogs. We're super happy to count you among us as vapers
I think the KFL+ is a great first stop for rebuilding. It is where I started as well. It will take a little time to get the hang of it, but once you do it is like riding a bicycle. I would suggest watching a few videos on how to make microcoils for it and make yourself a list of supplies. You'll need wicking material, something to wrap your coil around, and some screwdrivers, at the very least. The video will give you ideas on what you will want to use so you can buy it ahead of time.
Look for a mod that fires down to .4 and .5 ohms for something that is compatible with a Kanger Subtank. When I was shopping for devices, I usually looked at Phil Busardo's reviews (tasteyourjuice.com) as he goes in depth into how well devices perform at different ohms and under different loads. He's got super-long reviews, so if you don't want to spend hours looking at different devices, just scroll to the last 5 minutes or so of his videos for his thumbs up/thumbs down section where he gives an overview of all the things he thinks are good/bad with a given device. Of course, he hasn't reviewed all devices yet, but even just watching his reviews will help you learn what you like best or want to avoid the most when purchasing your new mod.
If you want to buy an authentic KFL+, I think they are worth the money, but if you are not sure that you'll like the Kayfun that much or you want to buy something more budgetary, the EHPro KFL+ v2 clones are excellent and perform near as well as the real thing. I bought one of those first, and then 2 KFL+ v2 authentics shortly following because I liked it so much.
Honestly, the Kanger Subtank looks like a decent atty but I don't think you'll want it as much once you start rocking your Kayfun... Additionally, if you are looking for a volume vapor experience, I highly recommend the eLeaf Lemo. It's basically a KFL+ clone with a few tweaks for giant airflow. Flavor is a little less than a KFL+ but again it's more for pushing lots of vapor. Only $40ish USD, too.
Best of luck to you in your vaping journey. Feel free to PM me if you have any follow up questions.