hi, K.!
i'm also a 32 year old first time stay/work at home mother to a 4 month old girl and i was concerned about the same issues. i'm one for letting her cry if she's just crying to be fussy. i can usually tell her fake cries from her real ones. i think you're correct to soothe your son when he's really crying (hunger, pain, diaper change, etc.)
i'm sorry i don't really have any good advice for you because my husband most of the time goes with whatever i want to do, but if i were to leave it up to him, he'd let her cry it out also. in the beginning, he would get very frustrated when she would cry for no reason and he would say, "i'm not going to have a spoiled child!" and let her cry it out. i just explained to him that it was too early for that method of disciplining and after a while, he agreed. still today, he sometimes will let her cry it out while i want to go in and soothe her. i don't know what kind of a person your husband is, but if he's anything like mine, he'll come around to your way of doing things....just give it some time and persistence.
good luck and let us know how things go.
p.s. i just want to add that i've never had a pediatrician tell me that babies will manipulate the parents at any age. i think that's kind of a weird thing for a pediatrician to say.