“Is it pretty easy to find taxis at the Florence train station?” Yes. The taxi rank is outside the front door of the station.

PS find the station on Google Maps and zoom in. You will see three lanes marked “taxi” and will see white vehicles in the lanes. Those are taxis.

"Another possibility is to walk, if your lodging is not too far away "

I agree - the walk to the centre (generally considered to be the Piazza del Duomo/ Piazza della Signoria or thereabouts)

I usually walk from the train station to Oltrarno (the south side of the river) and it takes me about 10 mins walk.

Easy to find, yes but you may have a substantial wait. We arrived in Milan the evening of 15 May (8:00 pm) and the taxi lines outside the train station were incredible and stayed that way for several hours that we were in the area to observe.