[fargle]

i have to agree with a lot of sibling comments: i don't think 6502 is a good pick. first, it's highly atypical and limited. second, it's borderline RISC and i'd start with a simpler to use CISC ISA. CISC makes sense and was designed exactly for hand-written assembler.

VAX or 68K would be cleaner CISC ISA to learn first.

8086 (16 bit) x86 has the advantage of being ubiquitous and you can run on "hardware" everywhere. but the disadvantage of being a little weird wrt. segment registers. x86 32-bit is complicated, but at least flat memory space and you can mostly ignore the segments.

MIPS or one of the RISC-V variants is a second one to learn to contrast RISC load/store with CSIC.