Hola John

1. This sentence that you are suggesting:  ¿dónde habréis estado en 10 años a partir de ahora?" wouldn't sound quite right. The fact that it is saying "...from now" in our English sentence implies that we can only use:

"de aquí a diez años" or

"en los próximos diez años" (and here the "from now" would be implicit)

What you are using with "en 10 años a partir de ahora" is very literal and it doesn't quite work in this case I am afraid.

2. 

Hola John

1. This sentence that you are suggesting:  ¿dónde habréis estado en 10 años a partir de ahora?" wouldn't sound quite right. The fact that it is saying "...from now" in our English sentence implies that we can only use:

"de aquí a diez años" or

"en los próximos diez años" (and here the "from now" would be implicit)

What you are using with "en 10 años a partir de ahora" is very literal and it doesn't quite work in this case I am afraid.

2. In reference to placement of adjectives, we have this lesson that will help you with your doubt:

Position of adjectives

I hope this helps,

Inma