the main use for chaintugs by most people is for easy setting (micro adjustment) of chain tension when a wheel needs to be removed and then replaced. You don’t and shouldn’t need a chaintug to hold the axle in place. The axle nuts should do that. If they don’t, then they need to be replaced. If you want to use chaintugs, realistically you only need one. Most people would place it on the drive side (side with the chainring)

setting chain tension and getting the wheel centred can be a fiddly thing, especially if you don’t have any experience. But it’s completely possible to do without any chaintugs. My advice would actually be to practice at home, at setting tension and centering the wheel. You should be able to develop your own way of doing it easily enough. If you need help, there are plenty of video tutorials on YouTube, and I think a video demonstration would be more helpful than me trying to spell it out in a block of text. Someone else might be able to chime in with an easy to read checklist of procedure though.

yes, the tension is set by “feel”. But the general rule is that it should have no more (or less, realistically) than half an inch of slack (up/down) movement. A little slack is much better than having it too tight.

Fixing a flat with the wheel still attached? Nonsense. Practice removing, replacing, setting tension and centering the wheel. Once you’re well versed, pulling the wheel off to fix a flat should be a quick, simple procedure.

obviously having to replace a tube would require complete removal of the wheel. This is why I said you should practice. Patching a puncture with the wheel still mounted, if that’s your thing, I’m not going to argue that. Do your thing mate. As far as axle nuts are concerned, there are two types, yes. I don’t know what type of nuts your bike came with, but a ‘track nut’ is basically a nut with a captive (floating/spinning) washer. It’s a captive nut. That’s it. And you should absolutely use captive nuts. If yours aren’t, then absolutely replace them. If you want to purchase a set of ‘track’ nuts, there are some more expensive and less expensive. I use shimano’s Dura-Ace nuts because they came with my hubs. Most people (and I would agree) would say they are some of the best. Retrogression (https://www.retro-gression.com/colle...rack-axle-nuts) has a decent set of track nuts for 5 bucks a pair. So 10 bucks for front and rear. You could probably buy a set of captive nuts at a hardware store, but you neee to make sure it’s the right size and thread pitch, and usually your rear axle is larger diameter than your front. (10mm rear and 9mm front)

you shouldn’t need to torque them down super hard. That’s where the captive washer matters. It bites down and holds. With captive ‘track’ nuts, you should be able to tighten down your nuts sufficiently without worry. And you won’t be putting down anywhere near enough torque, especially with a ss, to cause them to slip.

if you’re curious though, you could purchase a chaintug to practice with and without to see what you prefer. But you should have quality captive nuts, full stop. Everything else is just practice to get it down.

i have a very easy method of setting chain tension, but it won’t be helpful to you because my ss is a road bike conversion with older horizontal forward facing dropouts, so it’s not applicable for a frame with rear facing fork ends like yours.

As already said above, you can find captive ‘track’ nuts in the standard coaster and IGH 3/8” size. I wasn’t aware that you had a ss coaster hub, as I’m not familiar with this bike beyond the fact that it’s a folding bike. That’s my mistake for assuming it was a hub with a thread on ss freewheel. Nonetheless, all of my advice still stands. Most important of which, is that you should be using captive nuts. Cheers.

the nut doesn’t have to thread so far down on the axle, that you have axle sticking out past the top of the nut, when you’re dealing with captive nuts. Outside width of the nut is irrelevant. What’s relevant is the height of the captive washer and nut together. The mechanic at the shop will be able to determine if your axle has enough threading to safely engage the nuts they have. This would be a completely different scenario with non-captive nuts. Typically non-captive are taller (require more threading) than captive or ‘track’ nuts. Precisely because the captive washer means less threading is required to properly secure the nuts. So if your bike currently has non-captive nuts, that have enough threading, you should have plenty of axle threading for track nuts.

while you’re at the shop, ask the mecahic to let you tighten down a nut with a standard size wrench, to your strength ability and see if that’s secure enough. I’m willing to bet, you’ll be able to do it fine.