As soon as we declare independence, we're going to be wealthy.
Hey I'm pretty sure the UK could let you know a thing or two about aforementioned topic.
A separate currency
Oh yeah, just FYI, world market does oil trade in US dollars which you wouldn't have access to and would make selling that oil to US aligned countries really difficult. And the countries that aren't US aligned, they know that, so they'll be expecting deals for them or they won't buy your oil either.
I personally believe that our personal GDP will double in five to seven years.
That's going to be really difficult as you'll become more toxic than Chernobyl soil on the International market and Texas has no where near enough domestic trade to actually hit that 200% GDP in seven years.
But let's be frank here, an independent Texas would not go bankrupt. They have enough cash and product to stay afloat. But much like the US Civil War taught us all, that the Confederates found out super fast what happens when they get cut off from literally every market on the planet Earth. It makes it really difficult to keep that bottom line from going red and really forces governments to either make really difficult calls on how to govern their slowly decaying nation or start a war and try to convince the world that they should trade with them.
Texas would not crumble overnight but they would be hurting very badly economically. They would in fact be very poor. Very, very poor. If they think their oil is going to save them, go ask Venezuela how that's working for them.