Hi spiridijlqk2 and welcome to the forum
Whatever you decide to try first, just introduce only one new supplement at a time. This will help you to first see if you tolerate this specific supplement and have no particular side effect ( if you start many at once, you will not know which one is causing you a problem).
I think you have ordered a non-flush type of niacin ( niacinamide). Many members prefer to use the flush version, so they wait for the flush to occur, and then know it will be efficient for them. However, other members have relief with non-flush, niacinamide, or do not need ot have a flushing effect in order to be protected and have little to know POIS symptoms . In any case, B3/niacin has to be taken some time before release in order to be efficient. Since many members had success with it, it would be a good first try.
You proceed as you like, but in my case, I took at least a week or two with a new supplement, t o clearly see if I tolerate it well.
Also, if you intend to use them only just before and/or just after ejaculation, your test phase for each one will be longer ( because it is not a good idea to do frequent tests... the more release you have in a short time span, the more symptoms you will get... almost all members experiment this worsening effect, and almost all members, inversely, feel better if they have a minimal number of releases a month....).
If you decide to use some supplement on a regular basis ( for example, lecithin, which is a good source of acetylcholine, and some members has improvement with daily supplementing of eggs or other cholinergic supplements), it will take less time to test this particular supplement for tolerance. In the case of lecithin, you would also see in a few weeks if it helps with your brain fog, for example.
So, go slowly but surely, and see what works for you.