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I agree with the others. Your chances of ending up with a successful instrument are far greater if you go with something thicker. You can certainly save this top to experiment with later, though.

I use a fan braced design and go a little thinner than most (usually end up 2.1mm-2.4mm near the bridge and 1.8..-2.0mm near the edges). I don't use beefier fans but do a couple of things like using a fairly massive, solid and unscalloped lower transverse brace (ala Byers) that help me get away with the slightly thinner top.
I'd consider 1.4 to be pretty extreme and, while it is definitely possible to design a guitar that will sound good (albeit probably a bit different than most fan braced instruments) with a top that thin why lower your odds of success on your first go before really having a feel for what you're doing?

Save it for a double top.

_________________
Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Someone told me once that the difference between an amateur and a professional is how they cover their mistakes (that's any profession). If it was me on my first build with concerns on the thickness, I would get another top and repurpose the 1.4mm top that you have whether you use lattice bracing, laminated top, or a smaller guitar (or maybe a uke). You will certainly have more experience by then. Good luck in whatever you do.

I want to really thank everyone for their feedback it has been extremely helpful. As a new builder getting this type of experienced advise is really cool. A am building a small classical and it turns out my thickness target was a mistake. I now plan to make another top for my first build, however I will save the wood until I get more experience and will go for it with either a double top or additional bracing.
Thanks All