Secret nailing

[Daddy Boots]

I am replacing an existing 1880's softwood floor as the 168mm wide full length boards are not in good enough condition to strip. Room is 4.8m x 3.8m with 2inch joists at 400mm centre to centre above a full height ( 7feet)stone floored basement.. effectively a first-floor room. The adjacent open-plan area is a kitchen with a 7x24 gas AGA.
Made enquiries with a local specialist who is proposing BOEN flooring.... The oak sample looks quality... 21mmx 160mm micro-bevelled all round T&G with very few short planks.
He's been in the wood floor business 30 years and suggests keeping boards in the room for 3 weeks because of the AGA and relative low humidity, laying a vapour barrier aka a sheet of plastic and secret nailing to the joists and 10mm expansion gap all round.
Done some Googling and the general consensus seems to be you shouldn't go wider than 140-150 mm wide due to cupping etc and secret nailing should be done every 250mm plus or minus 50mm. As the joists are 400mm centre to centre and 350mm between is nailing 160mm wide solid planks straight onto the joists ok ?
All the skirtings off but the door architrave, marble fireplace and resulting threshold step into the kitchen area are putting me off laying 18mm ply as a base.
Any experience/comments/suggestions on what is proposed ?

 

[WoodYouLike]

Should be ok, but leave 15 - 16mm expansion gap around - 10mm for solid Oak in a room 3.8mm wide is not enough.

Also make sure every board connects with at least 3 joists.