Training & Nutrition - questions from a newbe

To preface, 20 years ago I rode the heck out of bikes but did not know why or what I was doing. I was 20 and full of energy. Now, 20 years later and 40 I am getting back into the sport/hobby and am approaching it from a more education possibly confusing attitude. I live on a county road that makes an 8 mile loop. Back in the day I would ride this 3 to 4 times a day making a 32 mile ride. Now after 3 weeks back into this world I am still able to ride it once, I am sure I could do more but as I said I am approaching it from a more formula attitude rather than ride till you fall down as I did 20 years ago. what I did last week was read about style and technique and tried to ride what I had read.. Damn near killed me. Average speeds, Peddling in smooth leg lifting circles and keeping a Kandace of 90 to 100 RPM... I thought I was going to have a heart attack!
Well today I made the ride again and just forgot all that and ran at my own speed and enjoyed the ride. I made the 8 miles and felt so good I kept going past my driveway and rode it again for 16 miles. I was not tired and felt good about it. My average speed was 10.7 MPH.... Now my question. What is better? To hammer on it and almost kill my self to build stamina or to take it easy and make miles? Because I think I darn near read rode and educated my self to death that last ride but I was able to make more miles taking it easy. What long term approach is going to make me a better road/ endurance rider that can keep up on club rides. I.E, I have no visions or goals to be a racer.

It will take about 500 to 1000 miles for your legs to be ready for fast riding.
After that you can push on your rides to the point where you are able to still talk and pedal hard.
That is what worked for me.

Paved or gravel road?

The easy answer is some of each. Two "normal" endurance rides, then one pushing-it ride. You might do one easy ride the day after pushing it. On the normal rides, also try to use better form. Don't pull up on the back leg, but do lighten the pedal. Pull back at the bottom a little and push forward at the top a little. Try to ride with a cushion of air between your foot and the sole of your shoe. Try to relax your legs, ankles, and feet. I know that sounds stupid, but it's true. Try to make one perfect pedal stroke that feels good. Then try to make two in a row. Etc. After a few weeks, you might be able to ride 100' perfectly. Gradually increase your cadence over a period of months. Don't worry about speed now. Try to perfect the art. Back straight. Only the sit bones touch the saddle. Neck extended. A helium balloon is attached to the top of your helmet. Shoulders relaxed. Elbows bent. Hands relaxed. Knees directly above the pedals. Ride beautifully.

I had a Five Mile Plan to start out with. You could have an 8 mile plan.

I would ride 5 miles, return home for a break. Go out for 5 more, Break, 5 more.

Got up to 50 miles a day with that method.

Passed the 1000 mark and one day met a group and joined them for 45 miles.
Struggled for 6 months to stay up with them.

Don't pull up on the back leg, but do lighten the pedal. Pull back at the bottom a little and push forward at the top a little. Try to ride with a cushion of air between your foot and the sole of your shoe. Try to relax your legs, ankles, and feet. I know that sounds stupid, but it's true. Try to make one perfect pedal stroke that feels good. Then try to make two in a row. Etc. After a few weeks, you might be able to ride 100' perfectly. Gradually increase your cadence over a period of months. Don't worry about speed now. Try to perfect the art. Back straight. Only the sit bones touch the saddle. Neck extended. A helium balloon is attached to the top of your helmet. Shoulders relaxed. Elbows bent. Hands relaxed. Knees directly above the pedals. Ride beautifully.

Fantastic. I love "try to perfect the art." Good to remember the next time I'm trying hard to keep up with the group. A friend of mine who was a Navy SEAL said when he was training they would say "Slow is smooth and smooth is fast." Your post reminded me of that.

What are you riding? Unless your planning on a really near term replacement you might consider getting the bike fitted. Even if it's the same bike you rode 20 years ago, you've changed and fit might be less noticeable to a 20 y/o body. The good news is that you don't mention any discomfort in your post.

What are you riding? -- The good news is that you don't mention any discomfort in your post.

It's a Pacific Coast Schwinn. I about have it set up the way I want it. The fit is OK.
I just don't want to start training in a way that will detrimental to me later since I am for all practical reasons, am again new to cycling.