I'm an old-camera-and-lens user.

Also, I like bright lenses, which may be even more important for studio work...

A 150mm f:4.5 or so is basic - and ubiquitous. Lots to choose form, and (dirt) cheap. At present, I have two Voigtländers: An APO-Lanthar and a Heliar. I once had a Schneider Xenar, but traded it (and a camera) for another camera. Schneider Symmar 150mm f:5.6 are also good (I've got one of those, too...), and they are convertible into a (softish) 265mm f:12.

You'll find that 150mm seems a bit wider than a 50mm lens on small format, so my suggested next lens will be 210mm. Again, I like vright glass - but those lenses come in #3 shutters which (depending on your system) may be too big for the lensboard. Old Compound #3 shutters will fit a technika lensboard (the closest there is to a standard); I don't know about newer shutters. Xenar is great, so is APO-Lanthar. The Lanthars are so good I sold mine, and spent the money on the 150mm same type, a 90mm Angulon, a Pentax Spotmeter, and still had a little left. Translation: They're EXPENSIVE.

How wide do you need - what are you used to using? Most of the time I find I need nothing wider than 135mm or 120mm. Old Schneider 120mm f:6.8 Angulon is a great wide-ish for 4x5", providing plenty of coverage for movements. An 80mm Symmar XL would be nice, but with the 2-3 times per year I feel one would have been useful, it's not going to happen.

Tripods are important. Maybe not as important as with 35mm (which need a lot more enlargement to make a decent-size picture), but very, very important.
Mine's a wooden one from Stabil (http://www.stabil.nu), a Swedish one-man company. Highly recommended!