Expiring mortgage, lease extension and staircasing

Akustik

I need advice on how to proceed with my current situation and it's a bit complicated to explain...

At the moment, I own a 25% share of a shared ownership (housing association) flat.
My fixed term mortgage is about to expire at the end of the month.
I want to staircase to 100% and extend my lease which currently has 60-61 years left.

The housing association has recently introduced changes to the informal procedure for extending the lease and they are as follows:

• 990-year lease extension term 
• Marriage value will no longer be applicable when calculating the lease extension premium for Shared Ownership leaseholders (MV is still applicable for all 100% leaseholders)
• Ground rent reduced to peppercorn 
• Lease extension premium based on equity share owned by shared owner

I'm kind of stuck in this situation of not knowing which action to take first.

There are so many questions that I'm unsure about:

1. Should I schedule a valuation survey before renewing the mortgage as I think the prices of flats in my area have dropped?
2. Should I extend the lease first, then staircase or vice versa? Which way would be cheaper considering the MV will not apply if partial share? Or should I do them at the same time?
3. Would I need a second valuation once I extend the lease and want to staircase?
4. Would extending the lease instantly increase the price of the share I don't own?
5. Should I go for a mortgage broker that's paid or one that's free?
6. Should I just renew my current mortgage from the same lender?

My flat's full price (3 years ago) was £200,000 with 63-64 years left on the lease.

P.S. Not sure if this is the right sub-forum, but the question encompasses several fields, so couldn't decide