Have you found a source for titanium tube?
I was looking at doing something similar a few years back and it was actually going to be cheaper to buy sheet and have it rolled and welded as tube simply wasn't available. I eventually worked out that there wasn't enough weight saving over steel to warrant the huge time and expense of trying to do it with titanium.
If I were going to do it nowadays I'd probably start by buying up various OEM titanium headers off Ebay and cut those up to get all the bends required. Tape it all together and take it to somebody to weld it all.
Not sure which were the first ti headers but the ZX6R had them back in '98.
The later they are though, the lighter they'd be.