The Stability Problem

Doing a track-stand on a fixed wheel bike is simple. Watch track riders stop at the top of the banking and wait there, trying to out-wit their opponents. It's reasonably easy to do a track-stand on a freewheel bike too if you use your brakes for a bit of help. Doing a track-stand on a recumbent is next-to-impossible.

The problem of low speed stability arises because you're stuck in the seat. You can't get up out of the seat and move your body around to help with the balance, to counteract any wobble. A slow-moving recumbent is an unstable recumbent. That's just the way it is. Slower than a threshold speed, and you'll fall over. Better just get off and push the thing. (With practice, you can lower the threshold speed, and you might even be able to do short track-stands, but generally slow = fall)

Hills

As with any bike, the traffic you just have to get used to. Hills though, takes hard work and lots of practice. The problem of hills comes about because of the big advantage of the recumbent - that wonderful, comfortable reclined seat.

You'll need to get used to do some serious hard work with your legs. Because you're stuck in the saddle, you can't honk, you can't get out of the saddle to push down on the pedals, , all you can do is keep those pedals turning. Some like to push the big gears, others like to get low and spin. Whichever, your legs are going to have to work hard. Sure, you can brace against the seat and get more push, but it's the legs doing all the work. Speed falls off as the gradient rises. Usually you'll be fine for balance (though you'll still need practice) as long as the speed stays above walking pace. Below walking pace, then you'll find it easier (and safer) just to get off and push. The gradient at which this occurs will vary with leg-strength and experience. For me, I can keep cycling on anything less than a 15% slope, but that has taken a lot of training and practice. If you are going to be climbing regularly, then it pays to keep the pedal release tension a bit slack compared to your normal setting, for those emergency releases which will occasionally occur. This is counter to the upright case where you have the release tension tight, so that you can pull up on the pedals as well as pushing down. When you're climbing on a recumbent, then you won't be pulling up on the pedals. It's all brace and PUSH

I was asked for advice about the StreetMachine I own. A friend was considering buying one, and had arranged for a test ride. What he was unsure about was the gearing. He lived in a very hilly area, and wondered whether he should spec a non-standard block, going for the lower gears. Nope, not necessary. If you're in the lowest gear, then you're at the limit of stability. You don't need lower gearing, because using a lower gear will put you below the threshold speed, and you'll fall over. If you really need the lower gear, don't. Get off and walk.

Mike Burrows maintains that even the multiple chainring is overkill. The Rat-Catcher which he designed has only a single chainring, though I have to admit that I'd find that a bit limiting. The philosophy is the same though - Low-speed is unstable. Instead of changing down, it may be safer to get off and walk.

Traffic

The second stability issue is negotiating slow-speed traffic. As you approach a junction where you may have to give way to traffic, the easiest option is often just to stop and get your feet on the ground. Depending on pedal, it sometimes takes a bit longer to get clipped in again, and traffic around you can often get impatient. You might want to try and keep going and get through the junction.
If traffic is heavy, then there's no option. Stop. If the traffic is lighter and you might possibly get a gap, then you might not want to stop completely - if a gap presents itself, then you want to be ready to grab the opportunity. Firstly, Use Your Ears. Listen for any approaching traffic. If it's quiet then you might not need to stop; if it's noisy then expect to stop.
As you approach the junction, slow almost to a stop, just short of the junction. Very slowly, creep forwards until you get a gap when you can go.
Such low speed stability takes a lot of practice until you get the hang of the balance. Practice in an empty car park until you get the knack of it, and make sure that you are capable before you go out in traffic.
Again, keep the pedal release tension set low, just in case you need a quick release.

There is of course a simple solution to all these stability issues.

Get another wheel.

Recumbent trikes offer total stability. Well. Not quite. In all the situations which I've mentioned above, the trike will offer you the stability and security you need. Can you fall off a trike? Yes, but only at speed. If you're cornering a bike at speed, you lean in to the corner. Trikes though have to keep all three wheels on the ground. Take a corner too fast, and the inside wheel will come up and you could then easily tip over. When cornering a trike at speed, you need to lean into the corner - shades of motorbike & sidecar racing, with the sidecar-man throwing himself from one side of the bike to the other in an effort to keep all three wheels on the ground for every corner.