The tilt-lock is not inherently dangerous and you should not fear it as long as you understand what it is and what it is not. It is not dynamite or nitroglycerine that can explode at any moment. Using the tilt-lock at a long stop-light to stretch the legs or shift around a little on the bike is not a problem. The only concern is to give it enough throttle that as the tilt-lock disengages that you have enough forward movement on the bike and that you, as the rider, have enough balance to keep the bike from going over. It is not difficult to master once you get a feel for the bike. HOWEVER, this is an individual decision that every MP3 rider needs to make
on their own based on knowledge of the risks involved, i.e. falling down, damaging your bike and yourself, looking ridiculous to those around you, and potentially being run over by a cager, as well as with their own comfort level and riding experiences on the MP3. This also applies to using the tilt-lock on the move while coming to a halt (another item that causes intense and heated discussions on this forum). It is not inherently evil to do this. It just needs to be an informed choice. My wife only uses her tilt-lock while parking the bike or sitting at long lights. She manually unlocks her tilt-lock with her feet down before pulling away from a stopped position. I am the opposite. Neither way is right nor wrong, just our individual, informed choice.
As to your other questions: Use of both brakes is a good idea in most circumstances. Exclusive use of your back brake will dramatically increase your braking distance as, per the discussions in most MSF classes, your front brakes supplies most of your usable braking force. However, using the front brakes exclusively will cause the front of your bike to dip causing a transfer of weight off the back of the wheel resulting in decreased braking force from the back wheel and an increase of braking distance off the ideal braking distance. Appropriate use of the back brake at the same time as the front help keeps the bike's suspension level with a reduction in overall braking distance since both tires are providing resistence to forward movement. Obviously, sudden overuse of the front brake on a down-hill could result in so much force transfer to the front of the bike that you and the bike go over. Going downhill, moderate use of the back brake and also engine braking are the best way to keep your bike under control. Add in a good dose of situational awareness and you should have no problems. The book,
Proficient Motorcycling: The Ultimate Guide to Riding Well by David L. Hough (available through many sources including Amazon and Amazon Kindle
http://www.amazon.com/s/ref=nb_sb_ss_c_0_11?url=search-alias%3Dstripbooks&field-keywords=proficient+motorcycling&sprefix=proficient+%2Caps%2C290) is a great resource and has some great information on this subject.
Braking in a curve may be a little bit more forgiving on an MP3 but the basic rules of riding from your MSF class should still apply in that you want to get the bike straightened back up before utilizing the brakes. The slope of the hill will compound any stopping on corners but if you keep your speed moderated (slow-medium) and your head on a swivel you should not have a problem.
As always, do not let anyone push you into doing something on your bike that exceeds your comfort level. If you continue to ride motorcycles (2 or 3 wheeled ones) your experience will grow and all this will become second nature.[/u]