Ransos – Probably don’t need the bleed kit but it was only £15 and sods law when adjusting the hose length it would probably need bleeding if I didn’t have one.
I would fit the longest drop you can get away with.
I was forced to go with 100mm drop as the bike it’s going on only has 17.5cm seatpost length from the top of the clamp to the rails and the 125mm is 19cm minimum exposed length.
Also bear in mind the location of any pivots that obstruct the internals of the seat tube when deciding on the overall length to be sure it’s not too long to fit down the seat tube.