First off welcome to the hobby, warning it can become addicting.
1. I'm not familiar with this brand and model but after glancing through an owners manual I believe you should start to develop a feeling for object depth with use based on the loudness of the signal and the amount of needle deflection on the meter. You may want to create a test garden in your backyard, clear an area of all metal objects - use your detector to be sure there are no nails bottle caps or pull tabs there, and then bury coins at various depths. Keep the coins well spaced apart 8 to 10 inches, and mark locations with plastic stakes or keep a well measured map of the area. Water the area, some suggest sprinkling a little fertilizer or salt to help speed up the halo effect. Then using your detector pass it over the coins to experience the difference of the different depths and sizes of coins. You can also do air tests by just holding the coil up and having someone else pass coins by the coil at different distances from the coil, but this will not be a true indication of how the coin will be detected in the ground.
2. Don't worry about storing your detector near metal, you could keep it in an iron box if you wanted. Once it is turned off, it doesn't matter if it is near metal. I keep one of mine in a storage bag, in my office, one on the back porch and a small one I keep in a metal drawer at my workbench. Take care of your detector, wipe or brush it down before storing it away and if you don't plan to use it for more than a couple of weeks I'd strongly recommend removing the batteries. You don't want to find that a battery went bad and leaked acid in your new toy.
3. I've never done any night hunting, but I know that there are people that prefer it. My favorite time for parks or possibly crowd areas is fairly early in the morning. Some people may think metal detecting is strange but it's really no different than any other hobby. Many newbies have this image in their head of the geekie-nerd walking along the beach wearing sandals with socks, a big over-sized hat ... and they are afraid of being seen in that light. But that geekie-nerd has a lot better chance at finding a cob, lost gold ring or other piece of bling. If you are going to worry about what other people think, then you choice of hobbies will be pretty limited, you don't even want to know what I think of golfers.
Don't worry about your detector not being a top of the line model, it's better to start out with an inexpensive machine to determine if this is a hobby you want to stick with. You will find things you like and don't like about every machine and the experience will help if or when you decide to upgrade. And a person with low cost machine that has had many years experience with will do better than somebody that is just learning a new machine. Good luck and I hope you have fun with it.