1. You should be feeding your Betta twice a day. You should be careful about feeding "all they can eat" in 2-3 minutes because it is common for Betta to eat much more than they should. Recommended foods are pellets made for Betta fish, frozen bloodworms, and occassionally a piece of a deshelled frozen pea, although not all Betta will go for it. Variety in foods and a steady schedule will make for a healthy Betta diet.
2. Betta need a lot of room to swim. If they do not have room to swim they will be less active and there conditions can take years off their lives. 5 gallons of wate should be minimun. 10 gallons of water is a very decent amount, but of course anything larger will result in a happier Betta. Always remember that Betta need LONG not tall tanks. Betta like to rest on the bottom of the tank, and swim back and forth. For them to be resting a bit on the bottom and have to swim a great distance to get to the top is not pleasant. It is also useless to have a tank that is really tall and really lacking in length, since they swim horizontal so much.
3. Betta kept in too small of homes usually only last around 2 years, 3 years if the owner somehow kept the water conditons clean. Maybe using products such as Amquel and Novaqua. Betta in 2.5g to 5g may live up to 4 or 5 years, with luck and good caretaking. A Betta in great water conditions and a tank 10g or larger could live up to 8 years, or maybe even more, but unlikely unless you're experienced.
4. Drinking water is not recommended and I don't know what drops you're talking about. If you were to buy 5g or more of drinking water that is very expensive as opposed to simply using tap water and water conditioners. Buy Amquel, Novaqua, Aquarium Salt, and Stress Coat. While you're at in, in fact, get Coppersafe, Melafix, and Pimafix.
5. It is okay, but your Betta might not do it in the first place. Maybe once or twice, though. Hell, one of my males nibbled a Styrofoam cup and another loved to attack a certain gravel piece. Just keep in mind that plant roots are not food, and also try and research the plant to find out it's requirements, such as lighting.
6. What is bad in your situation is that you seem to have left the food in there. You want to NEVER leave uneaten food in your Betta's home. It will rot and pollue the tank and increase risk of fin rot and other health problems. You read on the bad of the food package that it could take up to 5 days for your fish to eat, so i don't understand why you're asking this question. Give your Betta time to adjust. He can live weeks without food. Try feeding him each day. Give a single pellet to him and wait. If he doesn't gobble it up remove the pellet and try again the next day.
You really should have asked this stuff before your Betta was bought, in order to reduce stress and problems with your Betta. It sounds like you are a beginner though so I will admit when I was starting out with Betta I made the very same mistakes. You asked for some more tips/info so I will provide some.
I really recommend you get a 10g tank for your Betta fish. Doing so and giving him lots of decorations like sanitized or new PVC pipes, caves and also plants to explore will increase his happiness and activity. You should definitely have a filter for your tank, but be sure to get one with low current as male Betta are weak swimmers due to their long fins. A strong current may actually rin their fins. Along with a filter, a heater is a very good addition. Velvet, a VERY common Betta disease, is more likely to occur when the tank temperature is not steady. Not to mention when you treat your Betta for ich and Velvet, it helps a lot to have a heater around to raise the temp and speed up the parasite's lifecycle and get them to their freeswimming stage which is when the medicines do their job in killing the parasites.
Never put an air strone in your tank unless you've divided the tubing 4 ways and so there is little to no change is current from it. Your Betta may actually like the bubbles, but other than that it's useless to put it in there so you really just shouldn't.
If you believe that a 10g tank is too large for a single fish there are tank mates that may go with Betta. I will warn you know, though, a Betta is often times much less interactive with people when placed in a community tank. However, some things he may not notice too much and will still focus on you. Kuhli loaches, African Dwarf Frogs, and Pitbull Plecos are great additions. All active 10g fish come with at least a little tiny risk, but your best chances are Platies, Rasboras, and Tetra. To be brief, a 10g tank is a desirable one for your Betta. You can put tank mates with him with success, but he may become less "friendly" to you.
Wow I got cut off. lol. -edits out the rest-
