I know accounts have been banned, but as for it being mod related or for a payment issue, I can't say for sure. But they've been on forums in the past about banned accounts for the things that are bannable offense, and some that are oddly banned. It's still a risk though. So user be warned ahead of time. You know you shouldn't be using a mod for a game, but you take it at your own risk.
You can easily beat all the maps from 0.x - 5.x with E1 units at level 60 (as I've done so far. The only unit I have e2 is eyfyjlla). And using 3 to 4 star units is a viable option. It's just a lot of grinding. The units like lapland, or ch'en just make the game much easier because of how good they are post E1 40+. 5 and 6 star units are broken for the most part (depending on unit). But if you're playing because you feel you need the 5-6 star units, I can tell you now that there are tons of videos that don't require it. Before chapter 5 released yesterday, I was able to take my 3-4 star units up to chapter 4 in total without a 5 star unit, and ran it a second time with a 5-6 star unit once I had the route cleared to understand where the weak spots and strong hitting spots were.