First, the tank should be cycled. It's the most important thing in this hobby. A properly cycled tank will mean no fish will suffer.
Second, cleaning should be done weekly. A 30%-50% water change weekly. Also, if you decide to get the fish and let the fish cycle the tank, then up your water changes to 30% every other day, and test your water daily. Do not let ammonia or nitrites get above 1ppm. Preferably .5ppm or lower.
Next, I wouldn't recommend any other fish with the Beta myself.
Next, Either 1 male or 1 female. Your choice.
Not sure on feeding Betas myself if flake food would be ok as a main diet.
Next, acclimation. You need to acclimate the fish to the tank. It's fairly simple. First you place the bag in the tank, so it can acclimate to the temp. Leave in for at least 15 minutes. Once that is complete, you can acclimate to the tank water. You do this by emptying half the water in the bag in the sink, then slowly add some tank water to the bag with a cup. Do this til the bag is full, then empty half again, and repeat 2 more times. Once completed, empty the bag into a net over a bucket or sink and the fish will go into the net, then place the fish in the tank. Do not add the LFS water to your tank, you don't know what might have travelled with the fish in the bag.