1/ XGATE can see 64k of the internal memory. Paging is only relevant to the CPU and not to the XGATE. The XGATE can see up to 32k of the RAM - some of this will be visible to the CPU as paged.
2/ You can't change what you see in the 64k map but you can arrange your software in any way you like within this 64k.
3/ You have about 30k of Flash available and yes you can use all of that for code if you want.