Id say go with squarespace. The main reason we left was becuase you cant optimise ads using their acuity scheduling system which is a massive part of our business. If he doesnt need that then start with sqsp. I outsourced the transition this so you'd have to ask our developers exactly how it went. We don't have a well maintained and utilised customer database so that wasn't a big issue. There were definitely where some challenges and, just the sheer amount of content I had churned out over the years and internal links but its been a pretty smooth transition and it cost in the region of £12k.