Infant car seat vs. convertible car seat

My husband and I received a Graco 4ever at our shower, and now I’m wondering if I need an infant car seat also? We are planning to purchase an Uppababy Vista, and I thought we’d purchase the adapter and base for the Mesa car seat as well, but would it just be more sensible to just buy a second Graco 4ever for my husbands car? The vista comes with a bassinet for an infant, and I do plan to use a baby carrier while we’re out as well (at least that’s what I’m hoping). Did anyone use a 4ever from infancy-toddlerhood? Thanks in advance!!