First time doing gates, abit of advice please.

[Kent]

I personally would have made it out of angle if it's going to be clad in wood.

It's actually a door though. But yes it's cheap and effective to use angle
On a door like this I should do similar by using a shs casing but then adding edge on flat bar to the outside inner circumference
Angle could also be employed on box as it's easier to attach but leaves a rusting spot between the two sections

On a high quality infill style another flat bar inner frame could be used to make the second piece of bread in the wood sandwich. As a big ring picking up all the fixings

 

[armalites]

I think in steel it's less of an issue which way the diagonal is, the reason iis done that way in wood is a compression brace is always going to be more reliable then a tension brace due the fixing in the wood. Personally I think a diagonal starting at the top of the hinge side looks better.

A door made from 40x40x3 box isn't likely to have too many issues either way.

Don't assume that being at the end of a long track means things are any safer, sometimes that just means people are less likely to be seen doing stuff

 

[Kent]

Yes I agree it doesn't especially on a door about a 1000 wide or even more
I like the comparison with wood and the joint not pulling that might be why I much prefer that way
However a upvc door or window is always packed bottom corner hinge side to top lock side also
Let's face it welded in a brace ain't comming out either way

On a real big door, certainly a steel clad type you would put in verticals to horizontals
On a big timber Infill gate I rarely see any braces just suitable sections,. The infill itself becomes part of it - effectively a vertical brace

 

[Gareth J]

I agree that is doesn't make much odds here just didn't want the OP to feel his original design was at all "wrong". Far from it.