Great questions- looks like you are doing the right thing by finding out everything about your new pet before you invets in one.
Budgies perfer to be kept in pairs- they are very social birds and they do fret without a mate- if you are planning on spending at least 2 hours a day with your bird, playing with it and letting it out of its cage, then you can get away with having one- but they will become depressed if left alone for long periods of time without a friend.
If youre buying budgie seed, its a good idea to get the stuff from the local pet store- there should be less chemicals in it. Im not really sure what is the best commercial brand because Ive always been told that the pet store stuff is the best. You can also feed budgies pellets, and fresh fruit and veggies- which you should introduce to them early on- because they are not big on accepting change in their diets.
I am guessing that petsmart would sell both sexes in budgies. Males are better talkers and they also tend to bite less.
They sleep during the night- it is important that their cage gets covered up as soon as its dark outside, and the cover is taken off once it is light again- birds are very sensetive to light- their bodies respond to the amount of light in a room and use it to tell the seasons- if they are getting too much light they start to think its summer and begin to molt, and go into cranky breeding season- which you dont want.
You should name your bird whatever you are happy with- Bella is a fine name for a bird.
Spraying perfume probably isnt a great idea- I would probably do it in another room as birds have really sensetive respitory tracts and they dont really do well from being near aerosol sprays.
When it comes to perches, youre best just using natural branches that you find- they are good for your bird to chew, and the branches are different widths which is great for their feet- plus they are free! Steer clear of anything that looks like it could harm your bird if ingested.
When it comes to cages, bigger is better. Go for the biggest that you can afford that is suitable for your choice in bird. Budgies need a smaller bar spacing because they are so small, so you have to look out for that.
The cage you chose is ok, but I think its a bit small and im not a fan of the shape. All of my birds have open top cages for the day, and flight cages for the night.
good luck!