Can you tap the same land twice in a turn?
I think the other answer by doppelgreener puts too much emphasis on 400.7. I don't think that that rule is relevant at all. Rather, we have


  107.5. The tap symbol is {T}. The tap symbol in an activation cost means “Tap this permanent.” A permanent that’s already tapped can’t be tapped again to pay the cost. A creature’s activated ability with the tap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since their most recent turn began.


along with


  110.6. A permanent’s status is its physical state. There are four status categories, each of which has two 
  possible values: tapped/untapped, flipped/unflipped, face up/face down, and phased in/phased out. 
  Each permanent always has one of these values for each of these categories.
  
  110.6b Permanents enter the battlefield untapped, unflipped, face up, and phased in unless a spell or 
  ability says otherwise


So nothing in rule 110.6 says that a permanent remembers that it has previously been tapped; it is either tapped or untapped, and that's it. Nothing in rule 107.5 cares what has happened to a permanent earlier when you decide whether the tap symbol is a cost you're allowed to pay (except summoning sickness on creatures). Only its status in that exact moment.

If a permanent is untapped (regardless of why), then you are allowed to activate abilities it has with the tap symbol in the cost (unless it's a creature with summoning sickness). When you play the forest in step 4, it comes into play untapped as per 110.6b. You can then tap it to get a green mana. When it has been untapped by Kiora's follower, it is untapped, which means 107.5 once again allows you to activate its ability.