Help with Schengen Visa Application (Spain)

Hello everyone!

Could someone please help me with my application form.
Im Ukrainian, my husband is British, I hold UK residence permit (leave to remain) but it does not state "family member of EU national" so I know I need a visa.

We are travelling together.
We are going to Spain for a 1 week holiday in January 2016, and we would like to visit it again (or other EU country) later. But we don't know exactly when and for how long. That's why I'd like to apply for a multiple entries visa.

Question:

In the field "Duration of the intended stay" I want to write 90 days. (the longest for MULT visa)
But the the Intended date of departure, I'm not sure what to put. The date we come back from our 1 week holiday from Spain, or ....? Help please.

Field 21 mark other and write family member eu.
Field 24 multiple entries
Field 25 the number 90
Field 29 say 1.11.2015
Field 30 say 30.04.2016
Field 34 the personal data of your husband

and so on.