Swimming for fitness in addition to lifting weights?

Currently lift 3 times a week, and want to add swimming 3-4 times a week. Mainly just looking to get the most out of swimming fitness wise.

Unsure what my work outs should look like. From what I know about cardio generally I guess some form of HIT is more beneficial than just swimming at a steady pace.

My main questions are

1. Does it matter what sort of stroke I use? I generally just do breast stroke/not really comfortable with crawl (but can obviously learn.)
2. Any important pitfalls in terms of swimming/breathing technique to try to avoid? (assuming I don't care that much about my lap time just getting a good work out)
3. How long should a work out be and what should it look like. If its in intervals should I go by time or distance?

Currently in ok shape/not looking to lose weight.