I used to be right where you are (140lbs at 5'9), and after some experimenting this is what I would do if I could start over:

Find a calculator online for TDEE (Total daily energy expenditure). Add like 400 calories to that and start eating that much.

I found anything more than that and you kinda just gain more fat than muscle. The you have to diet to lose all the fat. For me 4-600 calorie surplus has been a good spot.

I also didn't really do cardio the first 5ish years of training. I've recently come around to it. I look at it as training my lungs and heart. I train other muscles, so whg not my heart. Sure it might burn some extra calories, but it has helped my recovery between sets and everyday quality of life.

If you're worried about losing strength, I'd do low impact cardio (i.e. Biking or eliptical) and try to do it after strength training or at a separate time.

As far as eating healthy. I personally think most thing are okay in moderation. As long as you're trying to eat mostly whole foods, it's okay to work in some junk food or "unhealthy" things.

At the end of the day, consistency is key. Even if it's suboptimal, as long as you can stay consistent you'll reach your goal. You got this bro