Hi I am biased and would say Libsyn.com is the best podcast host - it is where Marc Maron, The Nerdist, The NFL and many other big shows host.
Per your questions:
What is the most important thing to know when podcasting?
Be Consistent - release new episodes on a regular schedule - and keep to the topic you say the show is about. And most importantly - make it easy for your audience to give you feedback.
do I need a fancy recording ap for podcasts or can I just use my voice memos ap on iphone?
You do not need to spend a lot to sound good - but you do need to spend something. The Voice Memos app is not for podcasting - ever. Go with an app that can allow the export as an MP3 file if you have to do your podcast from your phone - Boss Jock - is the best app for Podcasters - as it allows export as an MP3 and FTP of the file to your podcast host.
If you want to sound the best - get a good mic - the Yeti from Blue ($95 at B&H photo) is a great USB mic. This you can connect to an iPad - but not to an iPhone.
Here is a link to a podcast 101 tutorial.