Absolutely use resistance on the bike. Use whatever resistance and RPM gets you working at the appropriate intensity.
Absolutely squat. Having a decent strength base, and the movement skills to do basic lifts well, will enhance whatever other athletic training you do.
Cardio is about training your body to use oxygen and glycogen, clearing lactic acid etc...
It's about many things, which are best trained at a range of intensities. But moderate intensity training prepares someone for higher intensity training. It's like with lifting - even if strength is the goal, you're not going to start off a training cycle with a bunch of 90%+ work.
If your not training near your vo2 max, your not getting much out of your training in neither those reguards....
The aerobic base is generally developed well below VO2max (Eg. 70% VO2max). The AT/lactate threshold is also below VO2max, so the lactic acid energy system is best trained a good bit below VO2max (Eg. 80% VO2max). On other hand, the ATP-PC energy system is trained way above VO2max (Eg. 170% VO2max). The percents are approximations, to illustrate a point, and vary based on a number of different things.
Additionally, the anaerobic energy systems are ultimately dependant upon the aerobic energy system. So if you're looking at a activity where there are multiple anaerobic efforts within a relatively short period, a well developed aerobic base is pretty important.
Steady state cardio has minimal effect on body adaptation until your into that time frame of over an hour, and even still thats not going to be a great deal help for you...
That's not true. There are so many studies showing positive training effects of steady state work with shorter durations.
Theres a reason marathon runners dont win iron man triathlons, the mile, or 400's....
And 400m runners don't win marathons. And sprinters don't win the mile. Shot putters don't win at BJJ. Etc. Someone who specializes in one sport not being able to win at another sport says nothing about the validity of using a particular aspect of their training for other athletes. You could just as easily say that powerlifters don't win "Insert sport other than powerlifting", so people training those sports shouldn't squat. But that's nonsense.
Your 40 and not an athlete and thats fine, but you cant be lazy and cruise fitness training and expect the body to adapt...
For the body to adapt, it just needs the training stress to be more than what it has experienced before, and the chance to recover. So if someone hasn't been regularly doing cardio, they can improve with just moderate intensity training. To continue to improve, training needs to become progressively more demanding. It's like if someone is new to strength training, they can start off learning technique with an empty bar, and since they're so new to it, they'll still get stronger.
Because most of your moves are explosive, you cant train your body to adequately recover for these explosive go/pause movements training a completely different way.
The bodies energy systems can't sense the "moves are explosive". They only respond to what demands are place upon them. It's only necessary to train the appropriate energy systems, and appropriate musculature.