Laying Reclaimed Solid Oak Flooring (22mm)

Hi,
I am looking for some advice. I have trawled the internet but with mixed results.

I am looking at purchasing 60m2 of Reclaimed Solid Oak Flooring (22mm) from a local company who specialise in this.

I plan to install it myself in my house, where I have just finished building a reasonable sized extension.

The area I plan to lay the floor is around 2/3 existing floorboards and 1/3 chipboard (in new extension). Unfortunately the new floor will be laid the same direction as the existing floorboards.

I realise I will need to lay some ply on top of this and to keep the levels the same I will need to continue the ply into the extension.

My question is:
What is the minimum thickness of ply I can get away with?
Should ply just be screwed down or glued and screwed?
Is it better to use portanailer throughout both floor types?
Should I also lay 2mm underlay to dampen noise?

All advice will be most welcome.
Thank you,
Mark

 

Thanks Gatt.

I have come up with a new plan; I just wondered what your thoughts are on the following?
The old part of the house is floorboards which are in good condition and are flat. I have just finished screwing every board at every joist to reinforce and reduce any creaks. The new half of the house is new 18mm t&g chipboard.
I now plan to lay the oak diagonally throughout the house (I appreciate the additional work and waste).
I plan to lay a 2mm foam underlay to further reduce any potential creaking.
I plan to secure the full floor with tongue tite screws as this is more convenient for me. I would need to hire a nailer over a few weekends where this way I can spend every evening installing screws which is less noisy and less expensive (I have done the sums). I also believe the screws will be better in the chipboard than portanails.
I guess my question is...
Does this sound a good plan?
Is there anything else I should consider?
Is there any harm in either using underlay or full install of tongue tite screws?

Thanks again,
Mark