I have to admit that I don't fully understand your question. Do I understand that your husband is great with older children but is really trying to muddle through the confusion when it comes to your new baby? Also that you want to make sure you are not sounding like you know it all when it comes to her? If this is the case then I may be able to shed some light being a first time parent.
Since my husband and I both were new at the parenting thing we were on an even playing field. However, because I stayed home with our newborn all day every day I learned quickly his temperament, needs, whines, cries, schedules, etc. I found myself telling my husband how to do everything when he was home and I quickly learned it was aggravating him and also insulting him. It was hard to watch him not feed him the way I did, not hold him the way I did, not rock him the way I did, not...not...not...You are probably seeing something familiar here.
First of all, any and everything my husband did never harmed our child and didn't cause any damage. Everyone has different ways of taking care or raising their children. I would have to leave the room so I could keep my mouth shut; this is how bad I was. It took me almost a year before realizing my husband was doing fine and the more I encouraged him or gave him praise for a job well done or told him what a great dad he was it made him swell with pride. For example, when he would get our crying son off to sleep after rocking him for nearly 40 min. or changed his diaper and not get pee'd on I would say, "great job honey, you are such an awesome daddy."
Since you do have experience what I would suggest is first a confession on your part. Sit down and tell him that you are sorry if you have made him feel like he can't do anything right or good enough. Tell him it comes natural to you to want to give advice since you had worked in an NICU but you know he loves his baby and that he really does a great job. Tell him you just want to make sure there is an open area of communication instead of him shutting down because there are going to be times as a wife and mom that you are going to have to call on him and you want to make sure that he feels o.k. with asking something about the baby or her care with knowing it's not going to make him look bad.
It's hard for husbands, who are suppose to be the bread winners, providers, and our knight in shining armor to feel that he doesn't know how to do something and the wife does. Make sure you take opportunities to ask his opinion when it comes to your daughter. For example I would ask my husband before leaving the house if I should take an extra blanket or what do you think about how many bottles to take with us? Do you think he is dressed warm enough or too warm? Better yet, I would ask if he would get our son dressed before going out and then I would talk to our 3 month old son (as if he understood what I said) and say �daddy can pick an outfit can�t he? And then tell my husband how adorable our son looked. After a while my husband would comment on the same thing. �Mommy dressed you cute today!� Any thing you can involve your husband in will boost his confidence and make him feel like he has a voice. Most importantly praise praise praise your husband. When we build them up they really rise to the occasion.