A lot is preference. An aider adds some instability (twisting, as well as difficulty getting big insulated boots to stuff inside a loop that may not want to stay open, in the dark, etc), so some folks prefer to minimize that by using as few aiders as possible. Some folks dont mind and do whats more efficient for them. It's also going to depend a bit on how athletic you are, ie can you easily take a BIG step up between sticks, or do you need to maintain a comfortable 16-18" distance between them.
I've used 1, 2 and 4-step aiders on just my first stick, as well as used 1 aider and transferred it between each stick. I've also got sticks with a built-in cable 1-step on the bottom of each stick, and I've done the same with tied 6mm nylon cord on the bottom of each stick. There are some prefab options that buckle onto the bottom steps and stay open, you can also buy cable ones that stay open. IMO that's the biggest help, is making sure whatever you get is easy to stuff boots into in the dark. In general the longer an aider is the less stable it will be, so practice to make sure you are comfortable with whatever you do--that's a decent reason to at least consider that if you go with a 4 or 5-step aider to consider using it only on the first step, at least to start with. At this point I like my cable aiders on each stick. It's not the lightest, but its relatively stable, secure, fast and quiet, and I have really light sticks so it's not a big weight penalty.
You can go to an outdoor store and buy about 15' of 6mm nylon accessory cord. Cut it into lengths so you can tie two knots in it and have about an 16-18" loop. Tie this around the bottom V-bracket on each stick, one knot below the V and one above so it stays put. You can put a 5" length of 1/2" black PVC pipe around the cord to hold it open. 3x an extra 16-18" per stick will net you an extra 4.5 feet +/-. That's a $20 way to try the aiders and see what works for you, and worst case you can use the remainder for a spare prussik (or 7). Either that, or here's a couple options, they have several differnt cable loops and aider options:
https://doublesteps.com/product-tag/aider/
You may find that practice will allow you to stack your existing sticks further apart too, if you want to maximise height. I use 4 short sticks with aiders, although occasionally I leave one on the ground if a set is better a bit lower. Lots of folks are into one-sticking and a variety of other specialty techniques, I've tried most and keep coming back to 4 short sticks, in large part for the versatility to adapt them to literally any tree, anywhere. To a degree relying on aiders is also something that can work great a lot of the time, but there are some wonky trees with off-angles, etc where its a bit tough.