Can't comment on the hip replacement, but your schedule is similar to what I do, though you're a bit ahead of me! I'm getting back in after a layoff, but I've been riding on and off for 19 years. Some years >3500 miles, some years zero.
Everything I say should be taken with the caveat that you should be leery of advice from strangers on the internet!
Your source seems to follow the rule of increasing no more than 10% in a week. I think that's very sensible, especially if you're starting from zero. Depending on how your weather is, building up to a 100 miler over the next 3 months seems doable.
What I found worked for me, building up, was a combination of things works best. I have always made my weekend rides about distance, so I go at a relaxed pace. Once I'm comfortable at a particular distance, I throw in climbs while keeping the distance the same, so for instance I started off doing a fairly flat 20-25 miles, then changed to a hillier route of the same distance. Now I'm almost up to 40 miles, and when I'm good with that, I'll add a serious climb. Once I'm comfortable with that, I'll add on to that.
Nothing but climbing can train you for climbing, but climbing will build your strength for other facets of riding.
For the midweek rides, I go harder. I'm trying to wear myself out in an hour, rather than keep going for 3. If you have some short climbs separated by flats, you can do hill intervals - push it hard up the hill, hard enough that you're gasping at the top, then ride the flat part gently to recover, then push it hard at the next hill. The hills should be no more than a 2-3 minutes really hard work.
Other rides, I'll do 'tempo', riding at a pace just below Lactate Threshold - so you don't have to pant, but nearly - on a mostly flat course for increasing lengths of time.
Then sometimes, especially if you worked hard on the weekend ride, you want at least one of your midweek rides to just be a gentle spin at low effort and a nice high cadence. Listen to your body, and it will often tell you what it wants, needs, and can do.
So, the answer to "Should I devote time to hills, shorter more intense rides, longer rides etc" is YES! all of that!