Maple back 1/8 - 3/16" is plenty.
I'm not sure the wood choices are best, others will offer advice.
There are two choices, glue in the reflex, or heat bend and glue in, or a bit of both.
You can't glue them and then put in recurve (AFIK)
A lot depends on your skill, experience, available tools etc.
You could prob start with 1/2" Walnut but would need to build it up for a riser section.
Not my speciality, but I thought I'd get the ball rolling... I reserve the right to be wrong!
Good luck
Del
PS Whereabouts in UK? I'm in Harlow Essex