I'm gonna go through that list with ya and tell you what I think
Disc brake kit with droupouts-pretty good overall
Reproduction monark fork-you may be disappointed, they're kinda cheap quality. Lots of people either make a similar thing themselves or they invest in a real one on ebay
Wheels- those wheels look pretty darn good, but you may also want to look at the husky and worksman wheels on pirate cycles. The worksman wheels cost a good bit but they are US made and VERY GOOD quality (I know a guy who was clipped by a car in the back wheel and it barely had any wobble afterwards
Dual pull lever- That's a standard price, I use them all the time, BUT that's not what you need for a brake light, there are little bitty waterproof temporary action switches that some members have successfully tucked under single pull levers so the lever pushes down on the switch and turns on a light. Just a thought!
Mirror-I've had experience with mirrors, that thing is cheap and little and looks cute, but you really need a mirror that goes up and out on a long stalk to see anything, or a bar end mirror. Just a suggestion.
Speedometer-I hate to say it but those speedometers are a joke. But if you are going with 26" wheels and cruiser tires, the speedometers made for whizzer motorobikes aren't too expensive and they actually work
The stem-It's a good idea to get a sturdy stem like that BUT, in the description it says 22.2mm in diameter be SURE that's the inside diameter of your steering hole because if it's not you'll be mad. An inch diameter is 25.4mm. Also it's kinda ugly, prettier ones can be found on ebay for better prices buy it now
Vintage plug wire-Those things look pretty awesome and are good quality. Go for it
Kickstand-may or may not be strong enough for the final weight of this bike. Kickstands are a problem for us heavy engine guys. My only advice on that one is to see what happens, but it may be worth it to fab your own.
The tank- Sportster tank will look almost silly it's so big, but you probably knew that. Up to you but I might choose a small tank for a minibike or moped that's in the sportster shape.
Throttle-that throttle is a very good option but let me tell you a little secret....come closer....If you go to your local NAPA and you insist that they have a twist throttle (called a throttle twist grip in their catalog) they will find it. It's all metal construction with a chrome and aluminum body and it costs $12.95 as far as I can remember. Check it out
Jackshaft, you may want to build from scratch, it will look cleaner and be a lot stronger, especially if you weld it into the frame.
Hope this has been helpful. Best of luck and happy buying!