If your not very good then I'd say start with a good team like Chelsea or someone like that. When you get better(both in gameplay and in career mode), then try a side like Southamton or the like. Maybe try playing with a team like PSV in the Netherlands, they are the best team in that league but there are other good teams as well. They are really young and can grow. You still get the challange of playing good teams in the Champions league but have an easier run in the league.
You can(for the most part) keep players on your side. You have final say(in most cases) which players leave your club. As long as you keep them happy with playing time and wages you should have no issues keeping them.
I usually play 6 minutes for my Youtube series with Fulham but in my other CMs I like 8 personally but it's all about personal prefrence.