I'm building a 10" D cell size can using a time tube and seven baffles 1 stainless the resthe are titanium. There will be a 3.5" blast chamber and it will have a 7/16 bore so I can shoot it on my 9.3x62mm.

Mat question is with a build this size how necessary is it to have the baffle stack welded to shoot calibers like .300 win mag or 300 Weatherby through it? I have been told welding is the solution. Or are there other limitations I don't understand?

How many of you have shot magnums through your form 1 cans? What happened?

Welding the stack isn't going to add inherent strength; on the otherhand, welding the endcaps would do exactly this. Regardless of whether you did or did not weld the stack, the same forces would be applied to the threads. If you would like to learn how to calculate this, and not be handed the answer, there are online thread strength calculators. You'll need to know your suppliers thread specs and do some searches for muzzle pressure of your intended round. I would recommend a SS liner for the blast chamber and, depending how much you shoot, using a second SS cone baffle. Additional weight will be minimal, but erosion will undoubtedly be delayed.

I'm not finding any sheer strength data for titanium. It doesn't help that I don't know what grade titanium I have either.

Most likely Grade 9, but could be Grade 2.
All the Fastener data, with calculators, here.
I'd be assuming that the endcaps are Grade 5, which is stronger than both 2&9; so you'd want to use the Maj Dia for your calcs.