Hi Stanley. Sorry, been off-line a couple of days. So, you have shot MF in a Yashicamat 124? Lovely camera, had a couple, they do become limiting for portraiture as you're stuck with 80mm only and can't get closer than a yard (which you wouldn't want to anyway with an 80). Although this IS the LF forum I'll be bad and ask why you need large format. If I wanted to shoot mostly portraits I'd seriously look at 6x7, Pentax or Mamiya.
For years I shot 6x6 in a C330S. For landscape and still-life I shot PanF, used a tripod and got beautiful quality. When I moved to 5x4 I was actualy disappointed in how little gain I achieved. With hindsight I'd have been far better going straight to 10x8. BUT- you want to shoot portraits. 6x7 would give you instant reflex viewing, 10 shots to roll for rapid working, ace quality, more choice of emulsions, smaller and cheaper enlarger. It worked for guys like Bob Carlos Clarke.
LF portraits? Yes, can be done, and can be exquisite, but ask what special quality YOU need which LF will add.
Go look at www.frankpetronio.com he's currently banned here ( and it also explains the 'is that you, Frank?' post earlier). Frank shoots LF portraits and has a real Love/hate thing going with the format. Also, search for a user here called Ash- young, student, UK based LF portrait shooter. Might PM him to get straight talking advice.