>I do not know if my code will be portable when I start learning it.
It won't be. Assembly languages are only portable to the processor family (and depending on the features you use, the family subset) they're implemented for.
>Do other Assembly languages conform to the same standards
The core concepts are the same across the board, and that's what you should be trying to learn. Don't focus so much on the difference in syntax because syntax is easy to learn. The hard part is learning how to program at such a low level.
>or is the Syntax incredibly different?
It depends. The difference between NASM and FASM is slight, the difference between FASM and GAS takes a bit of getting used to, and the difference between GAS and something like Terse is staggering. The most widely used assemblers implement similar enough syntax such that moving between them is relatively painless.
>Book recommendations would be great!
Since you're using HLA, The Art of Assembly by Randall Hyde would be helpful for the details of the language as well as the concepts of programming in assembly.
