Getting Fin to L20 isn't that hard if you often storm the maps with mounted units, leaving foot soldiers behind. Once trained up he, Cuan, Sigurd, Lex and Ethlin take over Ch2 in no time.
Levin x Tiltyu is overall better than any alternative due to the enormous Holsety availability, but Levin x Fury will do and is easier to make in first gen. If you do pair Levin with Tiltyu, pair Fury with Noish, or failing that, Claude.