Materials and design for Solenoids - R-02

[TMcRally]

Encouragement or criticism is appreciated... Thanks

I'm a few days expert in solenoids. Apologies in advance for my lack of knowledge and potential stupid questions.
It's my second post on the subject, thank you for your assistance in the first post.

The attachment is my "current" best guess to maximize pull power @ 12 mm stroke. It is a 10.30mm diameter armature.

Can I ask a few questions....

1. Should the meeting point of the armature and the core's cone meet; overlapping in the middle of the coil as shown in the diagram?
2. Should the brass sleeve overlap the core or is it better to butt up to the core and wrap the winding directly on the core?
3. Are the materials I have chosen most suitable (Quality is more important than cost)
4. I intended to use a high temperature winding, 240C does this have an effect on the number of coils or the power?

Thanks
Dave