next to > immediately after; _the arrangement is:

FRONT Sloth Gluttony
Avarice Lechery
Envy Wrath
Satan
BACK Lucifera_

2 Upon a bearded goat, whose rugged hair

rugged > shaggy

3 And wall eyes (the sign of jealousy),

wall > whitely opaque; glaring

4 Was like the person himself whom it did bear:

Was like > [Resembled those of]

5 Who, rough and black, and filthy, did appear

appear > (Or "appear:", meaning "seem", "present himself to view")