Seamless pipe is very expensive, and is only used in certain applications, such as steam condensate return, where ERW (seamed) pipe would not last as long. For a handrail, go with the ERW.
In order to connect a chromed steel pipe to a copper pipe, you will need a brass fitting. These two pipes will not fit into each other otherwise.
what is a type B handrail
It will connect to the PVC pipe into the wall which ultimately will connect into the main sewer line outside.
No! That will create intergranular corrosion
In plumbing it is a pipe connector that also reduces the size of the pipe so two different sizes can be spliced. If you want to connect a 1" pipe to a 3/4" you would put a 1' to3/4" reducer there.
NO but you will need some type of sealent OR braze or soldering
Yes
If the copper is big enough, you can treat it as if it were cast and use packing and sealant. If the diameters are too different, you can use a rubber coupling to connect the two.
Sweat a female fitting on the copper or use a compression coupling between the two.
This probably refers to a handrail that doesn't meet with the current building code standards.
Welding should only be done between similar metals. Installing welded flanges to connect two dissimilar metals would be the preferred method of connection.