To answer your first question:  No.  There is no reason to avoid HIIT at any part of your training program (note:  there are health related exceptions).  If you are physically healthy and are not taking any stimulant products such as coffee and especially "fat burner" supplements HIIT is going to be a potent stimulator to your metabolism as well as burn a lot of calories.

To answer your second question:  No.  High Intensity Interval Training is perhaps the best way to increase your cardiovascular fitness.  If you consider that at 10% body fat your cardiovascular fitness levels will be far superior to what they are now at 20-25% starting HIIT will help you reach your peak earlier and allow you more time to progress properly.

You need to make progress in your cardio fitness program just like you should with weight training.  HIIT is not something you will do every day while low and moderate intensity cardio is something you can do every day.  You should probably start off performing HIIT sessions once per week along with your low/moderate intensity cardio sessions.  As you progress your cardio fitness and get close to your fitness goal of 10% body fat, you will likely begin to eliminate the low/moderate intensity exercise and perform sporadic HIIT sessions along with weight training to maintain your fitness and sculpt your body to the "lean and toned" physique you envision.

Please NOTE:  before you, or anyone starts a HIIT program it is important to get a physical and a clean bill of health.  While HIIT is great to improve body compsition and cardio fitness it can take a toll on the body and if you're not healthy it's not unheard of that people drop dead while over exerting themselves during sprints.  HIIT is also great because it can involve a variety of activities.  You can find some interesting ideas for some simple, yet effective cross-training style HIIT on the following page: