Here are a few techniques that have worked for me in the past that I keep in my mind moving into the 2021 riding season.
Get your base miles in early. The earlier in the year that you get your first 1,000 miles, the more comfortable (and confident) you will be as you transition into warm weather group riding.
Heavier riders can crush the downhills if they want to. I do get an adrenaline rush while attacking a descent, but once you spin out on a big hill in, say, a 53x12 gear then your tuck and bike positioning for aero and safety are most important there. It isn’t worth it to go all out for maximum velocity if you are just going to crash (ask me how I know this).
For group riding and energy conservation, how about adopting more of a “domestique” supportive type riding at the back? When I have already gauged that you are one of the slower riders in my group, I concentrate on not talking and trying to get as much terrain riding the drops and riding a straight line and perhaps drafting on the wheel of a steady rider who ideally is a bigger rider than me. Now once that bigger rider realizes you are doing some energy convservation at his or her expense, you will have some payback due. If you can contribute a pull do it! But keep it controlled, don’t treat it like a hard pull where gaps are created. No one benefits from that. Once again, riding the drops and getting low recruits different leg muscles and let’s you up shift one to two gears. Breathe and count pedal strokes in cycles of 8 or 12 or mentally jam to a hypnotic funk tune or whatever gets you in a power zone. But end it quickly after say 50 to 100 yards. Flick you elbow and let the rider behind you pull through while you drift to the back of the group and back to energy conservation in the back. But keep your form and stay alert.
Sorry about you knees. I was going to talk about how to make your climbing less of a deficit while overweight. My skill building, fitness building here involves doing more mental (or even out loud) counting of 4 cycles of 12 counts. While standing/sitting/standing/sitting you way up the rollers. Just shy of the summit, I try to upshift one gear in anticipation of the terrain flattening, then work on breathing to bring the heart rate out of the red zone.