>>4312876I know the feeling from wetplate. It's always great to see the image appear when you drop your plate in the fixer. Very addictive!
A binocular reflex viewing hood is one of my favorite accessories for my sinar. It doesn't replace a loupe, but it gets close, no messing around with a stupid blanket, and it flips the image so you see it right side up.
For lens ranges I suggest:
90mm, your 210mm, a 350mm, and maybe a 150mm. Those will serve you very well.
If you go past 500mm you'll need to buy extra rails, front standards, a second tripod holder and tripod, and more bellows...
My suggestion is to get an older 65mm or 90mm super angulon like pic. Excellent lens for the price, and wide angle 4x5 is really great.