Hi,
Welcome to our forum and congrats on your new set of clip-ins. No questions here are ever considered dumb and long posts are very welcome. In fact, I am the queen of long posts. I even wear myself out reading my own posts. So please don't apologize. We love having you. 
There are so many incredible hair extension experts here on this forum I am sure they will jump in with suggestions but I will start with what I can suggest.
I am not personally familiar with the Fashion Source brand so I can not comment on the price you paid.
However, I personally think you were wise to go with the price you felt most comfortable with since this is your first set. I also think it is wise to pick hair that you liked the best (in terms of how it felt to your touch) since you will be wearing it on your hair. Trying to take on sewing in the clips could definitely be something you might want to wait on until you have had a little time to play with your new clip-ins and learn how you can best enjoy wearing them.
I personally think clip-ins are a great way for people to "try on" hair extensions without too much of a financial or time committment. I think you were very wise to trust your instincts.
The key question is whether the clip-ins you bought are Human Hair or Synethic (synth). You mentioned that you had the option to buy Remy hair but did not. If you are not sure whether you have synthetic or not, you may want to look at the packaging or call the store and ask them to clarify.
This is important because the vast majority of synthetic hair can not be styled with HOT TOOLS. This includes heated curling irons, hot rollers, flat irons or any type of heat. There is a secret way that some stylists will use an oven to change the texture of synthetic hair but it can be tricky if you have not done it before because if you are not careful you can melt the synth hair.
Human hair can be styled with any type of hot tools and it can be cut, colored, chemically altered and styled with products just like your own hair.
Synthetic hair can not be cut, colored, chemically treated or styled with excessive styling products or you will have lots of build-up which can become difficult to remove or will cause the synth hair to be unwearable in a shorter time frame. Synthetic hair does need to be washed with very gentle products to keep them clean. There are some great instructions here or post your questions and I know you will get some great answers.
I am sorry to hear that no instructions were provided. However, don't worry, you really can't make a mistake with clip-ins.
As far as the positioning of the pieces, don't worry about getting them perfect. Experiment with what pieces work best in different parts of your hair.
How wide are each of the clip-in pieces? I am thinking the longest piece would be the widest since it has four clips? Does the long piece extend from temple to temple? You mentioned a long tail effect. Is this from the longest piece of the semi-long piece?
Traditionally the shorter pieces are designed for positioning along the sides to help in blending the front hair with the back hair and the longer pieces for halfway between the nape of the neck and the crown for adding length as well as fullness. If the longest piece actually extends from temple to temple, definitely clip it in that way and play with getting it positioned to work the way you like.
Keep in mind that many people will use clip-ins to achieve volume as much as for adding length and may use the shorter pieces along the crown to add fullness there. They might also use the longer piece further down from the crown and closer to the nape for max length.
You might wear the semi-long piece you described either above or below the longest piece with four clips depending on where you feel it gives you the best volume of length, depending on what you wish to accomplish. Play with all the pieces and see what you like best.
You can wear clip-ins as often as you like although it is recommended that you remove them when you sleep or before swimming.
Extensions of all kinds as well as lace front wigs are extremely popular now. They are considered the hair accessory of the decade and women who used to hide the fact that they were wearing extensions or wigs are now very proud of them and love to show them off. Of course you should honor your own feelings but it is actually considered a fashion statement to wear add-on hair of any kind. If someone asks you if you are wearing a wig or extensions you can always figure out a way to answer them so that you feel most comfortable.
You can actually buy human hair clips in in various lengths, colors, textures, styles and those can be trimmed to match your current length. Another option is to wear your hair with the clip-ins and then pull it up into a pony or messy bun so it will be less obvious that there is a demarcation between your current length and your clip-ins.
It's great if you need to flat iron your own hair to match the texture and it is wise to match the textures before adding the clip-ins but please remember not to flat iron the extensions or you may cause them to melt.
As you move forward into the world of clip-ins you might wish to explore adding a few Human Hair clip-ins to any synthetics so that you can trim them, style them with hot tools and chemically treat them if you like.
I am so happy to hear you are excited. Hair Extensions are a wonderful way to transform yourself into a variety of looks and they are so much fun. Be careful though, they are extremely addicting.
Enjoy and please post photos and feedback here often so we can share in your new extension journey.