Based off my amateurish and still-in-learning modelling skills (which you can see in my portfolio), for environmental modelling, how much can I expect to ask for my work? I can work on it full time.
Big and small props, etc.
Just modelling, as I’m still getting the grasp for texturing and UV mapping 
Un-UV’d, un-textured models won’t get you anything.
I see, I’ll have to train more then!
£0/$0 unfortunately.
I wouldn’t even think about making money on your work currently, you have years of hard work ahead of you.
There are very skilled modellers out there already, struggling to make money.
I am not a modeler myself but have hired quite a few freelancers for different tasks. I saw some of the models and I would recommend looking at places like turbosquid to get an idea for what people are accomplishing. Also I would look at demo reels to see what the competition is up to. There are many factors that go into this but do not lose hope if this is your dream.
Thanks for your tips and heads-up 
My suggestion is to concentrate in one area at the beggining and get really good at what you do faster, i probably would choose whats most demading, then try other areas, it will be quite hard to be an excellent modeler, rigger, animator, scripter, game dev, in different engines. Unless your focus is to earn some with your own game projects, then be a generalist