You may not need the very best hardwoods available if you live in a relatively mild climate and you don't have animals or children that may be leaning or climbing on your ranch-style fence. Pick solid wood posts without knots, which affect the integrity of the post. Get post caps for wooden fence posts. Exposing the ends of the wood to rain will encourage moisture and cause rotting. Decide if you want to sink your posts in concrete or set them on fence post spikes.
Spikes are a lot easier to install and remove, whereas concrete is permanent.
Select a gate made of oak or cedar rather than economical softwoods. It will be worth the investment when you aren't replacing it every few years. Keep in mind that wrought iron requires priming and painting - and that painting must be kept up. Look closely at the warranties provided with any prefabricated fencing materials. Inc. How things get done.