Hi Chris,
here's some thoughts which may help.
When doing sit-ups do them "cross crunch" style.
Do exercises which strengthen both calf muscles equally, this is important because if your left side is weaker than your right it will throw your lower spine out as you walk. I know it did with mine because I wasn't walking "equally", and I paid a price.
Stay totally hydrated with some electrolytes and your back will love you.
Concentrating on walking "heel to toe" is great for your calf muscles and if you can get on a tread mill all the better. For me when I was walking I had to look straight ahead because if I turned my head I felt like I was going to fall.
I know our TBI's had an effect on our inner ears and thus good balance must be practiced every day and you can Google "balance exercises".
You can build up your left hand by squeezing a rubber ball, and if you're up to it you can start to learn how to juggle and practice with juggling bags which will help bring your left and right into balance. again you can google it.
Just sayn'