The choice to make cycling your main sport if you can run is not a wise one. It looks and smells like running, but for most it's really a dangerous, expensive, pain-in-a$$ mutant cousin of running. Save teh many $ and many hours and ER time, just say no.
Biking can/should be used as a nice supplement to running, but it has to be done correctly. The best way to do it is as a nice gap between seasons to let your connective tissues have a break and recharge the mind, but keep some fitness. Pick a couple of 1-2 week blocks in the year when the weather is good (biking is bad weather is a huge pain in the ass, the gear you need is staggering and it still sucks). Don't expect to get a giant workout, just go out and tick over the pedals, enjoy the sunshine for a couple of hours.
My recommendation is to get a cantilever cyclocross bike (which is what gravel bikes were called before marketing got involved) for like $1000, a jersey, helmet, shoes all for about $500. Find some gravel rals-to-trails (so as to not have death-by-car as part of your off season happenings). Waive to the hotties, crank tunes, ride to get lunch/coffee and just enjoy a few hours without impact.
If it's raining, skip the ride. Be opportunistic and think of it as a nice way to recharge the batteries but still get some exercise in.
That is all.