Hi!
Unfortunately, it’s hard to test flavors with a pre-made coil tank; it immediately takes on the flavor and then it’s ruined. I recommend getting a rebuildable atomizer (RDA) because there, it’s just a cotton change, and the atomizer isn’t thrown away.
You don’t need to overthink building your own; even pre-wrapped coils work perfectly for this purpose. Unscrewing two screws and threading new cotton isn’t rocket science 
Choosing flavors is, in my opinion, a long and difficult process for everyone. I recommend buying small quantities of the aromas, and don’t even mix more than 10-20 ml at a time.
I have no tips regarding the mod; just that its electronics aren’t the most precise.