Parts are pretty much interchangeable, since it’s just water. The standard threading is G1/4 and you will find that on pretty much all standardized parts and fittings. You can choose what size of tubing you want, any of the common sizes will be fine, just match the actual tube to the fittings.
From my experience, testing, and reading the testing of others my favorite parts in each category are:
Rads: Considering you want low noise, you would want rads that perform nicely at low speed, like 750rpm-1300rpm.
Thin: Avoid if you can, otherwise, the Alphacool ST30 performs soso. The Hardwarelabs GTS performs great but is water flow restrictive as fuck.
Medium: Alphacool XT45 ties with EK PE for performance, Alphacool has more ports for routing flexibility.
Thick: Hardwarelabs SR-2 does the best at the lowest speeds, and even remains quite good at higher speeds, but is overtaken by the EK XE by the 1300 mark.
Fans: Previously Gentle Typhoon or EK Vardar but if you have the cash the new https://noctua.at/en/nf-a12x25-pwm are excellent. All very close though. You will notice these all have a similar sickle shaped blade and that tends to be the magic. It’s a much superior design for pushing air through rads and staying quiet doing it. A cheaper option is the Arctic P12 fans.
Blocks: This is chip size / available mounting or GPU specific. I usually turn to the data. For Threadripper / HEDT sized chips as of the latest I can find, either the Heatkiller IV Thredripper, or XSPC Raystorm Neo Threadripper. The EK options are… ok. Aquacomputer and Alphacool are not very good.
Pump: Any D5 based option should be alright. I personally run the EK dual top PWM D5, but dual pumps is very overkill for a lot of things, despite the redundancy bringing with it a nice sense of security. D5s are known to be quiet and reliable. You might also see the DDC, which I have found the be quite reliable… at killing itself due to overheat at about the one year mark. Even the newest revision, and the older ones were worse, infamously so. That said I never gave any of mine (and I had a few) any airflow, something that the D5 does not need as it has a metal impeller casing and sinks its own heat into the water. There are other pumps, but except for one particular Koolance and one Swiftech, none of them are “high performance” pumps like the D5 or DDC, which would allow for more expansion of the loop later on. Other than that, some kind of speed control, whether it be just a switch (like on a Vario model) or PWM is a nice feature for filling.
Pumps Continued / Reservoirs: A very popular way to mount the pump now a days is directly onto the reservoir with a custom “top”. Which, speaking of, you mentioned not wanting. While it can be possible to run without one in a a few specific scenarios, you need at least some amount of standing water supply sitting above the pump in respects to gravity, as these impeller pumps need to be gravity fed, especially during filling. You do not want them to run dry for any notable amount of time. The old way was using a T line, but it is noticeably harder to fill. The other big benefit of having a reservoir is that they are nearly key in getting your loop to fully bleed its air bubbles easily. If you wanted to have your pump separate, something very small like a Swiftech Micro Res is an old classic.