First, get a 150mm lens (Well, 135 is OK too, as well as a 180 or even a 210mm, depending upon personal taste.) as a starter lens. There is plenty to learn and you will learn about the basics on how to adjust the camera much better with only one "normal" lens. While it's nice to have a few lenses, you will find that the whole process of large format photography in itself makes you concentrate more on the camera initally and after a while you will turn your attention to the subject. All of this with one single lens.
Apart from that a second wide-angle lens is a matter of personal taste, but a 90mm is plenty wide. Do remember that with the typical 90mm (Super Angulon or Grandagon or similar) you will have a generous image circle which will allow you to shift the picture up (most common) without disturbing the perspective. By the way, when you buy that wide angle lens, don't forget to find a fresnel lens for the ground glass. Without the fresnel you will end up in that common question: "My ground glass is too dark, will it be any better with that superlarge and superheavy f/4.5 90mm lens?" to which my standard answer have always been: "Get a fresnel! (Your f/8 lens is plenty sharp and plenty good.)".
I recon that you can find somewhere in this message that you don't need that many lenses, so a third longer lens could be a 240-300mm lens (depending on the length of your normal lens). But that would be by 2011 or so...
Don't get me wrong here, I do want you to have great fun with your new Sinar. But there is plenty to learn and you don't need too many boxes of stuff to find the hidden pleasure of large format photography. One of the things you may learn is taking the time to look at the scene/subject long enough to make the very best picture of it. LF photography is the main key to doing this, as setting up the camera takes a few minutes if you're fast. In terms of quality, it's quite easy to achieve similar quality with e.g. a Hasselblad in fractions of the time needed with an LF camera, so most of us don't use LF cameras for superior picture quality, rather something else. (You will find out it's very easy to goof up with an LF camera, much easier than with any other kind of camera you've encountered.) But again, have fun and learn from the mistakes.
//Björn
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