Hello, I may be able to help however it will mostly have to be without command blocks I am afraid. As I have a pretty good understanding of how most things work in Minecraft (Commands etc.) I have 2 ideas for you:
1. Try and save a thrown potion with a Structure block; Whether you get another player or a dispenser to throw the splash potion it may be possible to catch it with the structure block, since entities can be saved by the structure block (However I have not tested this, but it does work with falling snow.) , but you will have to be fast, this is when the boundary box and a button comes in handy.
2. Auto refill dispensers; Again using structure blocks, try saving dispensers which are full of splash potions and then loading them again in the places you want. Combining command blocks and structure blocks together can be really useful (I know this as I use them for my creative server in things like trolls and auto doors with bells :P), and using the radius command means the dispensers can automatically be refilled whenever the player approaches the area (The radius command can also be used to activate the dispensers). Let's hope you know a fair bit of redstone.
In case you didn't know "/give @s structure_block" will give the structure block to you.
I know I have said a lot about structure blocks in this but it's stupidly useful and even more stupidly unknown so I try my best to get the best out of it. :)
Hope this helped.
