Wow. Where to start.
You are not Avadon. 8x10 portraits are... a major learning curve. Exposure, lighting, perspective, DOF, subject movement etc.
4x5 portraits are not quite as easy as you think either. Jumping from MF is easy in some respects and quite challenging in others.
I shoot 8x10 because the tonal and intense image granularity blow me away, always have. But.. I started out with 4x5, lived with it for 20 some years, moved for a short time to 5x7, then found the camera of my dreams, an early 70s Deardorff V-8. And I still have 4x5 and 5x7 backs for it but they are hardly used. I use it to shoot landscapes exclusively. Contact print (8x10 - 5x7) only.
If I were you, I would buy a quality 4x5 monorail with full movements, a couple good lens, and a 4x5 MXT enlarger. If you really like LF, then go for the gold. Learn the basics first.
tim in san jose