If you're parents have that kind of attitude, then they definitely wouldn't notice you wearing a system. And it might be easier and less pain if you just went a did it yourself, and then maybe tell them after you have done it (they might scare you and discourage you from getting a system beforehand) especially if you have good results to show them and prove to them it works well.

- How often will I need to take it off, wash it and re-attach?

Once per week

- When I'm washing it, how long will the piece have to be off my head for?

Do you have your own room? If so, then it makes some things a little easier.

You could take it off before bed, get in the shower and wash the head and system, then wear a baseball cap incase anyone sees you for the remainder of the night. You don't need to take off the baseball cap (or beanie if it's a full cap) until the lights go out. In the morning get up before the other, get into the bathroom and attach (30 mins). If you have your own room you could do this in the room and that makes it even easier!

- Will I always need to have a spare piece handy, or will I only have to get one when I've been using my current one for a little while?

I only had one piece for like 5 months, so it can be done. But it's not recommended because they fade, so order two just incase.

- When I get my piece, since it will be a full cap will I still need to go to a hairdresser and get it cut in? Or can I just attach it straight away?

Yes, you need to get a full haircut. But you could attach it yourself, wear a cap (again) to the hairdresser, then get them to cut all those long hairs.

To be honest, with the style you are going for attaching will be easy. You are not exposing hairline and that makes a big difference. Just get the fullcap fitten on your head properly, get a firm attachment, and it's doesn't have to be 100% perfect.

You can do it It's all trial and error.