First time water cooling loop builder, need an experienced water cooling expert to check parts/compatibility

If this is a new build, definitely a m2 NVMe if you can price it out. Otherwise, get a good SSD. Also, more RAM is highly beneficial and I wouldn't do any build today with less than 16GB of DDR4 and at least an i7....depending on your camp, AMD alternative.

So, with that out of the way, shall we dig into this?

Pump: D5 is always a fan favorite, but I am also a big fan of DDC pumps, especially in series and even in series at different points in the loop. The MCP50x is a good choice. Much of this depends on whether you want to run a single pump, multiple pumps, and what size tubing you want to use. Of course, pump tops and fittings really kind of allow you to decide most of this.

Reservoir: debatable as to what you really want, here since it doesn't provide any cooling potential, it merely holds excess liquid and doesn't leak. Also, if you're planning to integrate your pump with your reservoir, good to see if that design is plausible, otherwise, tubing runs take care of that.

CPU block: Raystorm is pretty old, unless there is a new model I haven't seen lately - which is possible since I haven't been shopping around much. Don't get me wrong, it is/was a good block but there have been better designs since it was first released. WaterCool Heatkiller IV, Koolance 380 or EK Supremacy are usually considered some of the best blocks available. But, you're talking a few degrees C at most between almost all, and that is still partial to your thermal paste selection and application.

Radiator: XSPC RX360 is very old...like...over a decade old. Sometimes hard to still find stock, but is still a very highly rated radiator. There are better models but at a price. Alphacool's UT and XT lines are very good and relatively thick radiators. EK also has some good, similar contenders as well. HW Labs has the usual SR2 Black Ice which has held up well like the RX360. Check out the flow rates and fan speed delta charts here - http://www.xtremerigs.net/2016/04/21/xspc-ax360-radiator-review/5/ This is stuff that I really dig and also do when I have hardware to actually test...finding Delta-T curves and performance analysis.

Fittings: As long as you maintain correct ID/OD for your fittings and tubing, you should be fine, here. Not sure what all the extender and insert thingies are that you have listed, but I am assuming they are somewhat for your T-line, which might be a bit extravagant. A simple T-fitting and piece of tubing with a plug does just the same, or, just make sure you have a run that is low in your case, and when you drain, disconnect it. A drain line is often rarely used, even once, because if you're draining your loop for maintenance, you're probably going to be replacing tubing, anyway.

Coolant: I am an advocate for distilled water only. Dye or colored tubing if you want color. Otherwise, some sort of anti-microbial is essential to prevent growth. Killcoil is not needed - anti-microbial accomplishes this.

Here is my advice - if you're going to watercool, do it right. Skimping or buying cheap is going to leave you unhappy or unsatisfied down the road. If you have to plan out and buy components on a budget, do it. Find exactly what you want. In this day and age, watercooling isn't really necessary unless you're really cranking down on a CPU or GPU overclock, however, it will allow you to run a bit cooler even at stock. Is it rewarding and fun as a hobby? Absolutely - the entire reason I've done it for about 14 years. If you're looking for absolute performance from your PC, then use the watercooling money and buy better parts first, and then see what you want to do. Don't skimp on a CPU, RAM or SSD to save money for watercooling because what will happen is you'll end up with mediocre watercooling and a mediocre PC because your budget decided for both at the same time.