For the video I would recommend encoding at 640 x 360 - h.264 - .m4v format video - that works out to about 6 MB per minute or about 180 MB for 30 minutes. Don't go with HD video for podcasting - as most (over 50%) podcasts are downloaded to mobile devices and HD video is a bad end user experience during the download even with LTE. Going with the settings above it will work across all Apple devices that can play back video from iPod nano's to Apple TV.
With libsyn you pay based on how much you plan to upload in a 30 day window. If you are doing a mix of audio and video in a month - our App 800 plan ($40 a month) would give you 800 MB of new uploads every 30 days and should be enough for you. If you are doing less video - once a month - then the App 400 plan ($20 a month) would work fine.
let me know if you have any other questions off line - rob at libsyn dot com
Rob W
libsyn