It sounds like pretty normal behavioural development to me too, my DD2 is 4mo and is definitely becoming more interested in her surroundings especially when feeding - if her Daddy is standing behind me and she sees him while she's drinking, she'll happily break into a huge grin and leave me flapping in the wind
If she is having a reasonable amount of wet and dirty nappies, sleeps relatively well (quality vs quantity), and seems otherwise happy and healthy then she'll be fine (and so will you).
My first DD was bottle fed, and the most valuable thing that someone told me was that if I had have been breastfeeding her I wouldn't know how much she was getting in millilitres and would have to use other signs to assess how well she was at any given time. This has still certainly held true for my DD2 who is exclusively breastfed.