You seem to be coping amazingly well. Congrats on getting through the surgery.
What lies ahead is a completely personal pathway. Even if you have full use of cognitive and physical function, its going to take a while to recognise and develop strategies for dealing with changes to your neurological functioning (mood, memory, decision making, thought processes etc) This whole diagnosis stuff also takes it's toll emotionally. This is a life changing event, a fork in the road. If you want (or need) to go back to work urgently, that's fine, there are people out there that do go back to work, but give yourself time to adjust to your new world. If you can manage financially to not work while you are receiving treatment, then dont rush back to work. Take time. Smell the roses. Enjoy your family. You need to learn your abilities again, because you will be affected by surgery, radiation and chemo. One of these days (and god willing, no time soon) you will be on your deathbed and I bet your last wish isn't that you wish you went back to work faster after your brain cancer diagnosis.
I don't believe it's helpful for me to comment on your diagnosis, that's an issue for you and your treating team to discuss. Aside from that, obviously grade 4 tumours have a worse prognosis than grade 3. I've seen a study that had grade 3 astrocytoma survival at 30% at 10 years! So don't write yourself off just yet. A lot could happen in 10 years - and even if they don't find a way to cure us, ten years is too long to live preparing for death. Having this damned thing in your head is just a thing you need to cope with in your life, and that has its challenges, but in the end it's just one experience you will have in the fullness of your life.