Supergas sound bonkers for a 5 hour walk. Why would you do that to yourself?! They're terrible for your feet.
I've had a lot of walking dates (I started dating someone just before the first lockdown). To be honest, it feels like we've walked everywhere by now! We're usually out for 4-5 hours so I always wear something comfortable and with decent soles. Sometimes that's trainers (proper trainers, not Superga/Converse etc) but now it's winter, I usually wear some very substantial (and on trend) boots. He calls them my"bovver boots".
I just ignore him. They're comfy, have thick soles and I can wash the mud spatters off them. I wore dresses sometimes when we were walking in the summer but it's bloody cold and often raining / windy now. You really need to wrap up and dress for the climate.
At the moment I wear leather (or fake leather) leggings a LOT as they keep my legs warm, I can move freely in them and they also show that I have fantastic legs.
But I met him in my gym so seeing me in leggings is hardly a novelty. I would LOVE to wear more dresses or skirts (and some 'real' shoes) but it's just not very practical outdoors in December, even for city walking.
I wore a maxi skirt (with the boots of course) a few weekends ago and regretted it at the point when we were sheltering under a tree from the torrential rain in the park and I really wanted to sit down for a few mins. The rain was constant and we were stuck there for ages. But my skirt would have been ruined so I didn't. I kicked myself for having a "must try and look more feminine" moment when I got dressed that morning.
Should have put my leggings on! A week later, in more torrential rain (it was sunny when we met up!), we had take shelter in an open shipping container. No skirts that day thank goodness!
Actually I find the hardest thing when we're out walking for ages is finding some public toilets that are open! Mainline rail stations have become a saviour.
So OP just wear something comfortable - and weatherproof - for the time of year. If he likes you, he really won't mind what you're wearing. You think he's worrying about what he's going to wear?!