a. when this league finally gave up their mutual status and became a limited company, it was the last to do so. Which club?

b. in 1884 this club was the first to use the formation 2 fullbacks three midfielders and five forwards. Which club?

To be honest mate, I don't understand the first one.

At a guess Nottm Forest?

oops, I'm not surprised you don't understand it, the word club should be the 4th word and and finally should be the 5th

Nottingham Forest is correct, on both counts

other Forest firsts: the first team to give the referee a whistle, instead of waving a white flag (dunno the year), the first team to bolt a crossbar to the uprights (in 1891), and in 1921 they were the first use round goal posts instead of square ones

I've never been able to confirm this: Is a Notts County v Forest derby game the oldest in world football?

I honestly don't know mate. I imagine it is. I'll ask a couple of the Forest fans that I know.
Incidentally I don't support either Forest or County. I support Mansfield Town!

Didn't know the one about the goalposts, will remember that and try it out on a few people.