Timber Gate Build

I want to build a garden gate for a double gate opening.
The gate I already have is a 1800x915 feather edge board gate that is strong as hell and I want to reuse.
The said opening is 2450mm from wall to wall, so with 2 100mm on the ends and a gate of 915mm that means I need to build a gate of 1335mm wide.
What I'm asking is what size or type of timber should be used. I have some C16 45x70 would that be strong enough or should I use something else.
I wish to put 100mm feather edge board on the top and use 3 450mm hinges. I intend to put the posts in deep holes with concreate and fix the posts to the walls with 10x160mm frame fixings.
I've bought wickes treated kiln dried C16 timber 45x70mm &45x95mm lengths.
How should I join the timbers, mortice/tenon or 6 x 150mm single thread screws.
Joined like a stud frame.
My existing gate, that I want to fabricate a new larger one to match.

Missing pic?
Kiln dried timber will not be suitable, you need pressure treated timbers.

Its treated timber.
http://www.wickes.co.uk/Wickes-Treated-Kiln-Dried-C16-Regularised-45x70x2400mm-Single/p/166401

Open mortice or lap joint will do.Will need treating before hanging to avoid early warping and rot.

I've never tried a mortise/tenon join, I'm not a very good at sawing and chiseling but I do have a sliding mitre saw, plunge router & track Plunge saw

Router would do the job.