To answer your question miwinter:
Thickness = higher moisture content. The thicker and wider the planks the higher the moisture content and therefore greater post fitting movement.
Glued or nailed?
The old rule is that engineered can be glued and solid wood cannot, solid wood should be secret nailed (always nails, never screws, explained below).
The reason for this is that solid wood has a higher moisture content ability than engineered and is therefore going to expand and contract. Nails allow the natural minute movement of each plank. PVA glues (and screws) hold the wood rigid, and PVA is usually 'stronger than the wood itself' (to quote evostick) so this does not allow for any movement, resulting in risk of the wood bowing or even splitting.
However, with narrower and thinner planks, I would advise maximum size of up to 85mmx13mm, you CAN get away with gluing as these narrower and thinner planks have a lesser amount of moisture content. But the caveat I apply is that this is dependent upon the moisture content of the room you are installing in.
Concrete Floors
As far as concrete floors are concerned, I dislike solid wood planks fitted directly to concrete. When I say directly I mean over a type of membrane, bare concrete releases moisture continually so you must ALWAYS fit a suitable membrane even if fitting a battened floor.
If you are investing in solid wood planking you want to feel its benefits over engineered.
Firstly, being that it has more compression and so feels softer underfoot. Solid wood laid directly onto concrete loses some of this as there is no flex compared to when fitted over joists or battens.
Secondly, conduction of heat. Natural wood feels warm to the touch, but when laid onto concrete its overall temperature will drop and it will feel colder underfoot.
The risk is that the end result of solid fitted directly over concrete is that you may as well have fitted less expensive engineered wood.
Battening
Be aware when laying battening, enough so you don't experience bounce, but not too many or the floor will be rigid.
Spacing of the battening is dependent on size and thickness of plank, thinner / narrower planks will flex more than thicker / wider planks and will require more battens.