Hi fd3, welcome to recumbents.
I don't profess to be an expert, being only 3 years and about 2500 miles in, but IME it's all about miles, experience and confidence. The latter comes with the other 2.
It took me about 500 miles to feel that I had the leg muscles to propel my Performer Amigo - a 20/26 tourer style 2 wheeler. Maybe 500 miles after that, it felt reasonably 'normal' after years of riding a DF bike. I use it as my light shopping/bad weather/winter roads bike as it's on Marathons.
Then I took the decision to commit to recumbents and scavenged my Giant road bike for its wheels and gear set and bought a Performer High racer frame set and built that up. I've audaxed the Amigo, but it's the 200-300k audaxes I'm after. That's a whole different can of worms. Higher BB on the 700c machine means higher seat, so less confidence at the stops, and no suspension means bumpy rides and poorer forward vision (vibration) - so confidence took a hit, not helped by more 'sensitive' steering, and a severe 'off' with a front blowout and a landing on gravel. I now wear elbow protectors......
It does get easier, but you have to put in the miles. It's a whole new experience, but the rewards are worth it. I saw newly-returned swallows a couple of days ago - because by looking forwards rather than at the tarmac (on a DF) you see what's around you. Then I wondered why a crow was attacking the top of a telegraph pole, until I realised that the top of the pole was actually a buzzard. Magic. And then a guy accosted me after my café stop in Wem to talk about the High racer - a tandem rider as it turned out. And, after a relaxed 50k, I had no back ache, no sore wrists, no complaining from my palms, and no numbness in the gentleman's area. At 62, minimising the effects of ageing is a serious objective, believe me.
So, it's all about miles. Try to get out 2 or 3 times a week, and build up confidence in starting and stopping. The hills will come with the leg muscles. Plan ahead so you don't get caught out at awkward junctions in the wrong gear to set off again - indeed, work out what gear you need to start off in a range of situations (uphill T junctions are very tricky) and then make sure you have got into that gear before you stop. IME, you need much more forward planning on a 'bent. It's a whole different ball game to riding a DF, but, IMO, it's well worth it for the different view (more trees and sky, less tarmac) of the environment we ride through, and the much reduced wear and tear on our ageing bodies (well, mine anyway). Isn't that why we ride bikes?
KBO, as Churchill reputedly said.