If you have 4 or more Ranger levels, you may swap your Animal Companion for the ability to learn more Ancient Temple maneuvers and stances.
How many?
It's on the next part, "At 4th level, and every Ranger level thereafter, you may remove a spell from your list of spells known to learn an Ancient Temple maneuver or stance of a level no bigger than half your Ranger level, rounded up." So basically one plus another per extra Ranger level.
and recover each exended maneuver as a fullround action
Do you mean full-round action per expanded maneuver or full-round action for all expanded maneuvers?
One fullround action per maneuver, a la Swordsage.
Also, I'd like to refluff the discipline to not be Touhou themed. Any good ideas what skill to replace Profession (gardener) with and how to change the fluff of some of the maneuvers that create mini-gardens or flower petals?
Depends entirely on the campaign and character's theme you want I guess. You could go Profession(cook) and leave behind meals. Or Profession (house designer) and leave behind furniture and decorations. Or profession (blademaster) and leave behind artistic slashes across the terrain and tiny sliced pieces instead of petals.
Basically any kind of profession that would involve bladed tools.
You could change it to a non-profession skill, but then it would not only be a refluff but actually a bit of power up if it ended up being a skill that matters for other important stuff like Spot/Listen. Also would make it harder to think of something to alter terrain into.