Fatbellyboysstuff:I'm currently about 260 lbs at a height of 5'9" (176 cm), so if your weight is still accurate I'm about 40 lbs heavier than you.
one thing that surprised me the most about my gain was how quickly I've run into accessibility issues due to my weight. I still consider myself relatively small compared to other feedists, but I already can't find clothes in store anywhere near me and a lot of furniture here is rated for 220 lbs max. so even though I don't feel super big, society is definitely letting me know that I'm getting " too fat".
I'm still fairly active, though I don't work out in the traditional sense, but I do walk about 6 km every day and I can pretty easily do 10-12 km if I want to. what has definitely been a game changer since getting fatter, is splurging on good shoes. my daily shoes are now trail runners and they actually help so much with not getting too much back/ joint pain when I have to stand or walk a lot.
as for the more directly physical experiences- be prepared for your fat "getting in the way" of various things. one thing I never anticipated was that my belly makes it hard for me to reach my sink to do the dishes. I either have to stand at a really awkward angle or put my belly on top of my counter in order for me to reach more comfortably. bending over is also getting increasingly hard, so I often find myself opting to squat down if I have to pick something up from the ground. I'm sure there are more ways in which my belly impacts my mobility/ functionality that I can't think of right now, I just know that every so often I can feel myself doing something differently than how I used to do something and it's always a great reminder of how big I've been getting.
have fun on your gaining journey!

Thanks for your reply! My weight on my profile is about accurate, maybe a few lbs more since I updated it, but I haven't checked yet.
I will definitely "steal" your suggestion of looking to get some good trail runner shoes! I usually haven't really thought about what kind of shoes I wear, but I probably should since I deal with some back pain. It's also nice to know that you can still be fairly active with walking without necessarily working out in a more typical sense. I imagine that too helps when it comes to back pain and preventing it from getting too bad.
I have yet to experience my fat getting in the way of things like that, the only thing I can no longer do is touch my fingertips on both hands together at my back when I reach with one over the shoulder and one from below, which I used to be able to, so I can no longer scratch my whole back myself without a scratching stick. But I'm looking forwards to reaching a point where a few more things like reaching the sink (didn't actually think about this one) and bending down will also become a bit of a challenge, and to find out if I want to gain more once I've reached my goal or not (330lbs).
Thank you again for your reply! I hope you have fun on your gaining journey as well!