Will be around 51,5 mm because the exzenter (BB)'s diameter is 51,3 mm at the flanges.
If that would be possible (I don’t know) then you’d still have the problem of missing width - the Strida BB’s are just around 58 mm wide, I guess (?)
Sure, you can use the alloy BB.
Yes, I do think so; never heard of a broken alloy BB, but plastic ones did break (occasionally).
There are just two items which separate a LT from an SX - these are the wheels and the excenter.
To avoid misunderstandings; the ATS excenter of your link from bikegang - this is a dual speed excenter and it fits only the ATS (or Schlumpf) speed drive.
Dual speed and single speed excenters are a bit different!