I've seen the site, I've not seen the kit, I've read through the PDF, and I used to own an original KIM-1.
I am not an electronics expert, but assembly of the kit seems straightforward. You can also buy it assembled, but frankly I think it should be simple enough to make it worth putting together.
I never had mine hooked up to a teletype, I just used the keypad and the cassette interface (which always seemed to work just find for me). I actually still have the tape around here somewhere. Mostly I keyed in programs from the First Book of KIM, and dabbled with lighting up LEDs off of the I/O lines. Pretty sure I fried one when I shot 9v into it one day. It also pretty much turned the TV to snow whenever I turned the thing on
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I think if you're mostly interested in software, it's a pretty cool piece of kit. Having the serial port handy so you can use the TTY portion of the KIM monitor is a bonus, because you can use that to save and load programs (via your terminal emulator) so as to not have to fuss with a cassette tape.
But you can still dabble with hand assembly and keying in things through the keypad. The keypad interface worked, it was much better than the switches on the front panel of an IMSAI -- that was simply painful. But I bet you may fall in to simply using the keyboard over the keypad.
You can use an assembler to create programs, but you may have to write some simple scripts to convert them in to a dump format that the KIM can understand -- I imagine that's pretty trivial work.
From a hardware point of view, what I like about the Micro KIM is that for $100 + a soldering iron and multimeter (and maybe a power supply not sure if it comes with one or not), you (ideally) have an up and running, compact 6502 SBC.
You don't need the other paraphernalia that goes with building circuits from scratch: wire wrap sockets or bread boards or PC board designs. You don't need an EPROM programmer (or some other mechanism). You don't even need an assembler on day 1 just to get the thing started and lit up. Get it on Friday, I bet you're up and keying in programs sometime on Sunday.
But, if you find you like the hardware stuff, well you can always grow in to that. It comes with an EPROM, so you can wipe it and put something else there, or just burn a new one. The chips are socketed, so you can use them in your own design. You can build an expansion card and make lights blink or add a SD-Card reader, or whatever you like.
In this way I think the KIM, plus this site, can be a gateway in to getting more into hardware. Early, incremental successes, with a low up front outlay of dollars and time. Probably get everything you need from scratch for $200.
The "worst" thing about the KIM, in contrast to perhaps a custom machine, is that the ROM and I/O are in the "middle" of the memory map, $1700-$1FFF, whereas on most other machines, that's all crammed up at the top end of the system.
That's an idiosyncrasy of the design, and you'll likely not be able to change that without some significant hacking. But by that time you'd probably be comfortable enough to just start over and wire up something from scratch.
I've thought about it, I haven't pulled the trigger. I may well still do this.
I was perhaps where you were, and I instead wrote my own simulator, that helped scratch the itch in interesting ways.