The Greenline BC-106m is an almost identical bike to the Micargi and I've seen no bad reviews of the greenline frames. It's what I used for my Military Bike Project
. Obviously I went a little beyond the call of duty with the junk I added to mine but the basic frame is sound and good for an easy build.
The only downside I would add is that I think you will want more braking power than the coaster brake alone that these cruisers come with. In my link you can see I added caliper brakes but I eventually removed those and got adapters to add v-brakes to the bike. You'll appreciate the additional stopping power.