We were open to everything during the exploratory phase. To be honest, however, the "work of the tenders" somewhat deterred us from an architect. Well then: I pored over catalogs, clicked on every googleable house company on the internet, simply to see if there was a house that we might like. Potential changes to the roof planning, facade, and floor plan were considered. A free floor plan was important because I did not like the standard floor plan for an average house size in 99% of cases. We wanted a ground-floor room in addition to the spacious living area, and less upstairs (there are just two of us). We then decided on our construction company. We are building with an architect who runs a regional construction company as a family business.
Now a tip from experience: I realized that many things would not be possible so quickly (bank, finances, building application, insurance) if I were not sitting at the office PC and could not make calls in between my work. Imagine if I worked in retail or on an assembly line... I would go crazy having to organize everything at home in the evening. I would not be able to call anyone or arrange anything during the day. If it is the case for you that you are not flexible during the day, then in your place, I would hire a BU. If you are happy with normal standard :)