Or: either 

misconsters: misconstrues, misinterprets

humorous: temperamental; Elizabethian medical theory taught that every part of the body was composed of four elements (earth, air, fire, and water) which gave rise to four 'humours' or temperaments

more suits you to conceive, then I to speake of: can be more fittingly imagined by you than expressed by myself

smaller: 'taller' in the Folios; Edmund Malone's correction

his malice 'gainst the Lady: Le Beau swears that soon, Duke Frederick's hatred towards Rosalind will reveal itself suddenly (foreshadowing how Duke Frederick will exile Rosalind in the next scene).

bounden: indebted

smother: slow-burning fire