1. I know what Xant means, and in general cardio directly before or after weightlifting is not beneficial for muscle growth and regeneration, while light 30-60 minutes of cardio at the "no workout" days is beneficial for regenration.
But it's totally fine to do 15 minutes of light cardio before and/or after a workout, as long as it really is light and short.
I personally only do 5-10 minutes "cardio" to warm up the whole body before my workout, then rotator cuffs with stretch bands and local/muscle specific warm up with light weights. In total not more than 15 minutes of warming up. 45-60 minutes of light cardio a week, sometimes less, depending on time and whim.
2. A 3 day split is only a thing for intermediate lifters/bodybuilders with advanced strenght and some experience.
Also a 3 day split would mean at least 5, preferably 6 workouts per week, which is pretty heavy and only doable by advanced gym goers, if optimal muscle and strenght growth is your goal.
If you just want to get in shape and get/stay fit a 3 day split with only 3 workouts per week is fine, but you won't make any noticable strenght or muscle gains after getting the "noob gainz", because the frequency is way to low.
Protein-bio-synthesis only lasts between 24 and 72 hours after hitting your muscles, so for getting otpimal strenght and muscle gains a 2 day split with 4 workouts per week (A B A B ) is the optimum for intermediate lifters, total beginners should always start with a whole body workout 3 times a week.
