FCOM, FCTM has the guidance on Vapp just follow that. There's a provision for pilot adding extra speed but it's not for tailwind. TW increase GS which increases the ROD so a little early flare is recommended. Generally problem with long landing starts with too much initial flare. It's a visual judgment you should be breaking the descent by half i.e. 350ft/mt appx. and continue towards touchdown point and reduce a little more at 10ft. Executing direct to there's no point reducing speed, if the new track is in opposite direction you may stop acceleration by selecting speed.
On takeoff Flap optimum setting or company recommendation can be used.