In terms of front shock, I would not go above 100mm. You can probably put a front disc but not a rear assuming there are no rear disc posts. I’d go with 9 speed. Only the Sram XX are 10 speed. Replacing the rear shock will be hard since it’ll prbably be a shorter length than what you can get on the market. You will need to measure from eyelet to eyelet and then the shock stroke length. I suspect 6 inches with either 1 to 1 1/2 inch stroke. Fox may make a shock like that but the tuning may be off. If the stock shock is still working, I’d stay with that.
Go for Avid mechanical disc brake. They work great and use standard V-brake levers.
Hope that helps.