We all wish there was some golden recipe, strategy, tactic, diet, or a plan to follow that would GUARANTEE results.
Sorry, but life isn't like that. Rarely can you use someone else's tactics and apply them directly to yourself and expect the same success.
Finding the best lifestyle patterns for YOU is a game of trial and error. Sure, we can quote the Canadian Society of Exercise Physiology recommendations of 150 minutes of moderate to vigorous activity per week, and set that as a goal. However, if you're starting from 0 minutes of exercise per week, this is a HUGE step forward!
Better to set more achievable goals with incremental improvements rather than huge leaps and bounds.
When it comes to lifestyle change, the first question is to ask yourself: For how long do I want this change to last?
If the answer is that you only want the change for a short period of time, the sure, you can go on a fitness binge or restricted diet.
If you want things to last, then it's better to go slow and steady.
-Be a tortoise, not a hare-
To answer the initial question: How much should I exercise per week?
If you're exercising under 150 minutes per week, make a goal of exercising 10 more minutes this week. Add an extra 5 minutes per week until you hit 150 minutes each week.
If you're exercising over 150 minutes per week, keep it up! Think about your health goals, and find ways to exercise that are more focused for your specific goals.