Pretty nice challange!!
First you have to watch the forces created by the F5d- style flying, as mentioned the G-forces are a main part but at a wingspan of 1400mm and the typical F5d wingarea torsionforces may be your neckbreaker!!
years ago we build some F5d Flippers for F5d limited competition (800g) with oracovered balsaskin with foam core out of the mould as it was required by regulation, we did not pay much attention at the spar,( if i remember right we just took steped 3 or 4 rovings at top and bottom but we used carbonweave underneath the balsa shell!
Just check out a typical F5d wing, its a carbon -balsa- glasfibersandwich with a solid spar.
Maybe its possible to get such a sandwich without a mould, i think the foam core will be the best way to get it.
this (german)thread may give some inspiration:
If necessary i can translate.
The 2/3 has less wingspan with slightly higher wingarea so airfoil is thicker and stiffness is less challenging.
But it is able to performe 220mph at 1,1 Kg even with a nervous stickfinger(but sure with less than 35G!!)
To be honest, i dont think you will be able to get the same performance in corner or topspeed than a moulded F5d but if you would manage to get somehow close it may be much more satisfying than just buying one!
If you need help with spar dimentioning or other F5d buiding technics just ask!