Buy your parts from
https://us.hkwebshop.com/ . It will be much cheaper than any reseller, and the shipping isn't bad. I don't think you will, but if you need a part number that doesn't come up on the search, just call them and they'll get you squared away.
I don't have time right now to be OCD and look up all the part numbers and links for this post, but it's easy. Brownell's or google work.
At the bare minimum, you need a left-side control lever. I prefer the decocker-only, which is the detent plate you have. You might consider whether having a lever marked to indicate a safety function is present when one is not present is a good idea, and select parts accordingly.
You may be able to find someone who has installed one or more LEM kits and has the V1 lever and detent plate sitting around and will sell them cheap, but most peoples' ideas of what their spare parts should be worth is likely to be based on hkparts.net usurious pricing rather than
https://us.hkwebshop.com/ what-it-should-cost pricing.
As noted, do all the springs. Find the most-recent version of the spring chart and pick the ones you want. Use a nickel sear spring for sure, as it's better in multiple ways beyond just being a little lighter. Rebuilding a recoil spring assembly is pretty doable if it is for you. JRB would have no problem with it, I didn't when I did it. But the non-spring component does wear. Inspect yours, and if the guide rod has a noticeable amount of wear/peening on it, it's probably better to just buy a complete assembly. HK says the longer spring needs changing only every 20-25k rounds, and the shorter one as needed (if I recall correctly - I posted about it sometime last year when the conversation was fresh).
There are how-tos around for detail stripping and for smoothing the parts. I don't follow them exactly, as I have acquired my own tools and techniques for that kind of work. Importantly, no rotary tool, such as a Dremel, has any place there. But the online guides are useful for getting oriented. Some of the pieces are a little fiddly, but none of it is difficult. There are no press fits (well, the sear spring snaps into place, and the mag catch has a slight interference fit with its roll pin if you mess with it, but you don't need to), you just have to get the sequence right. (This is my experience as someone who has rebuilt manual transmissions and engines, and is not universally shared.)
It is recommended to get the trigger return spring pliers, though not totally necessary. I like to dress the ends of the TRS legs with a stone so they slide across the plastic, rather than digging in and carving a groove, when installing it. Just be hyper-careful not to scratch the coils, or it will break prematurely at the scratch.
The big expenses in the Match kit are the overtravel stop trigger and the hammer. The overtravel stop is a bad idea for a defensive gun. The hammer differs from the standard hammer only in the cut of the SA notch; it will give a shorter creep and maybe slightly lighter press in SA, but will do nothing for the DA. The Match kit overall is officially not recommended for defensive guns. The rest of the Match kit is just a few springs that are available separately and inexpensively. Anything the Match kit does to improve the DA will be done by those springs. (See the spring chart.)