Ok, for firsties, grab a cuppa, and sloooowwww dowwwnnnn.
I'm glad to hear you're already onboard with sencha. Den's has a few inexpensive teapots you might want to look at. However, if you're looking for something nicer, Artistic Nippon's Tokoname
section is a great place to find well-made Tokoname kyuusus.
Den's is a good place to start, then maybe 'move up' to O-cha. There's not really a hierarchy between the two, but Den's is better for beginners because you can order in 2oz sized instead of getting whole 100gram bags.
From Den's, I would recommend the Green Tea Kit
, which is an awesome deal. If you want to add more to that, pick up Den's Guricha as well. mmmmmmm.
If you'd rather go to O-cha, then I'll tell you, it's hard to go wrong.
From O-cha's Sencha section
, everything from the Otsuusan and up have been loved by people. I would skip the Daily green tea, as well as the organic. The three you listed are all awesome teas, very intense ones. I doubt you'll be disappointed with any of them.
By the way, Welcome to TeaChat, and GOOD LUCK!