so i just did a 2 hour "solo" run (by solo i mean chrom pairing w/ fe mu), and it took all but 2 hours, no grinding involved. then i got inspired and did the same thing on lunatic in about 6 hours. Also note that its not really possible just to use chrom+mu only until after the chapter where you have to protect his sister, but that chapter i just used my characters as meat shields to protect emmeryn. after that chapter i did grind the free dlc chapter to get chrom to lvl 20, but after that no grinding whatsoever.
so, thinking about lunatic+, is even possible to do a chrom mu only runthrough (after the emmeryn defending chapter). i am also assuming you would use forged aversa's night, with armsthrift, luna/sol/ignis, tomefaire, defender, and veteran(replaced by i don't know what once you max stats) on a sorc mu, with +def, -str (it worked for me on lunatic). and also chrom would have pally as a final class.
the only chapter that was annoying for me (after the defend emmeryn chapter), was endgame, where i was basically invincible, but the dang healers would heal grima, and just lucked out with criticals from mu and chrom to finish grima.
so tldr, is lunatic+ possible with chrom+mu (after a certain chapter of course), and what is your suggested setup?