Why do online tire places suggest the LX in most years use
a R15 wheel but all the other trims a R16 , can I use a 16" if I have a LX ?

 

You can do what ever you want.
Just abide https://www.willtheyfit.com/ and pay attention to the inner bore diameter, and offset.

 

Was thinking of buying these used Austin Mini wheels , the bore size and bolt hole pattern match , theres just no info on the offset . Was thinking of plastidiping them white .

 

The LX came with a factory 15" steel wheel, the EX came with a factory 16" alloy wheel. There's no difference in suspension/brakes though, so both cars can take either size. Knope's link will be useful if you want to go much outside the normal range, I think I've seen people here talk about using 14" for snow tires and 17" for looks, although that will give a really short sidewall.

 

Was thinking of buying these used Mini Cooper wheels they are 16s and bolt hole and bore size matches