I would do a coating every 12-18 months. Some sealants drop off quick on certain conditions and vehicles it seems. you have to consider your maint plan afterwords as well. If you do a coating I suggest if you want to hose wash your car to use carpro reset. Rinseless I would use d114 by meguairs, Wolfgang uber is great as well but will take on the beading characteristics of that temp after using it, which isn't a terrible thing but it's not a coating.
On the flip side if you like to wash your car traditionally with a hose you could always use one of the spray on, rinse off sealant/coating deals, Hydro2 by carpro is what they sell here, there are a few others out on the market too, but you will have to use it more often, like every 3 months, it is pretty darn painless though. And every nook and cranny is protected.