Sex life and family planning

1. Are we allowed to plan our families (say that we have 3 kids and don't want more for whatever reason, and practice NFP)?

2. Are we allowed to have oral/manual sex after reaching that decision, or after reaching the age when the wife is not fertile anymore or cannot bring a pregnancy to the end without serious health risks? Is oral/manual sex in those situation a mortal sin?

3. When considering openness to new life - does that apply to Catholic sex life in general or should we apply it to every sex act at a time?

4. Sex is here for procreation and love. Should we prefer abstinence (and fulfill none of those purposes ) over oral/manual sex (and fulfill one of those purposes)? Of course, when a married couple with children is in question...

Thanks in advance