Players can't take any actions between the time you choose whether to tap a creature and the time Redcap Raiders gets +1/+1 and gains trample.

While resolving the ability of Redcap Raiders, you can't tap more than one creature to get +1/+1 more than once.

Tapping an attacking creature with vigilance to pay the cost of Redcap Raiders's ability won't cause that creature to leave combat or to stop attacking.