My idea was to have a rollfilm back with it to cover mainly 6x7, and some panoramic shots on occasion maybe.
If I'd buy a standard lens for 6x7 than I also cover wide angle for 4x5 was my idea ... did I figure right here?
I guess coverage is the main concern. the 100mm schneider & rodenstock do not cover it, so I guess I have to move to 90mm grandanon or something...
Yes, that logic works. The 100mm lenses are very nice for 6x9 and smaller (rollfilm) formats, but they won't work for 4x5. 90mm is (arguably) closer to being 'normal' for the 6x7 format anyway. I like the Schneider Super-Angulon 90mm f8 a lot on 4x5, and it will work well as a 'normal' lens for your rollfilm back too - on which it will allow a huge amount of movement. The earlier 90mm f6.8 Angulon that others have mentioned is also a nice len, and much lighter, but it is not (quite) as sharp and has much less movement potential when you use it on 4x5 - they also aren't all that cheap any more. There are other 90/8 options, including a nice Fuji that is no longer made. Anything faster will be easier to focus, but will generally weigh a ton.
Your 150mm is a nice length as a 'short-long' lens for the rollfilm back, so you have that covered.
For a 'short-long' on 4x5 the 210mm is usually suggested. It's a nice length and used ones are plentiful and reasonably priced - but you may find that it seems a little bit closer to the 150mm length than you want. If you are really trying to maximise your flexibility from a small number of lenses, you might want to consider whether a 240mm would be more useful to you. This depends on your shooting style and subject preferences, of course. For your rollfilm use, on 6x7 think of these as the (35mm) equivalents of about a 105mm and a 120mm respectively.
That would give you a very useful 90-150-210/240 kit for 4x5 use. What you then don't have is a wide lens for your rollfilm back. Most lenses that will do that duty are quite expensive, but the old Schneider Super-Angulon 65mm f8 is fairly reasonable and also quite small and light for a wide. I think I remember there is a no-longer-made Fuji 75mm f8 that is also good and very compact. Both these would also work as extra wide lenses on 4x5.
A really cheap option for a rollfilm wide would be the 75mm f4.5 Tominon from a Polaroid copy camera: this is a sharp reverse-Tessar designed for macro work on 4x5, but sharp to infinity when stopped down: it will just cover 6x7 at infinity and you can get one for peanuts.
Ask if you want any other suggestions. I use rollfilm backs - including a Sinar Zoom like yours - a lot, as well as 4x5, so am quite used to thinking about lenses that will work on both.
Peter
