It's best not to mix cardio with a workout... so if you are going swimming... don't workout straight afterwards as it impacts the amount you lift and it's not very effective...
Also, don't do it the opposite way around as your muscles are fatigued and you won't be able to get a good cardio session...
as far as I know it's ok as long as you break them up... eg... keep them about 2-3
hours apart....
4 sets x 12 reps?
Why not try 3 x 8.... that's supposed to be the most effective according to a book I have here... doing too much sets creates a lot of lactic acid and increases catabolicism (or whatever).
hope this helps...