Any lube that says it is for chains should do fine. I use many different ones because I have only been biking for 3 years and am in the process of finding my favorite. Some here even use their own mixture of motor oil and some stuff but what I currently use is Finish Line Wet Lubricant that is green and smells minty (I think) and it good for less dusty conditions since it is s little thicker and dust can stick to it. It works well and lasts a long time. I also use it to lube up all the moving parts of the RD that some here may use Tri-FLow for instead.

Yes, stuff does normally loosen up, but usually over a period of time or a lot of riding. For example, chains stretch and there are break in periods for shifters. Brake pads don't work the best right away. Saddles are uncomfortable right away. Some pedals take time to loosen up. I adjust things when I hear noises or feel that it is off.

There is a general maintenance that I have in one of my bike's manuals and it suggest weekly wipe down and lube of chain, monthly cleaning and check/adjustment of drive train (RD/FD/etc.), and yearly total bike cleaning. I personally overhaul a whole bike every 6 months of so and leave it alone in between and suspect that recommended schedule is for racers or people that really put in a lot of miles or maybe ot make LBSs money.

P.S. I use White Lightning for my road bike which is a wax based lube that creates a waxy coat over everything so dirt does not stick. It is not as smooth as petroleum based stuff and because the wax wears down with friction, you need to reapply it quite a bit more, maybe every 50 miles or less instead of a lot more. I did not do that and my chain rusted so yea....