First of all, welcome to the game!
1) The modules are available at this url:
http://www.paradigmcampaigns.com/DefaultLivA.aspx You get to the downloads themselves by registering, clicking "Adventures", and then creating an event (home game, FLGS game day, whatever you wish to call it). Once the event is created, you may download any of the (at present) 11 adventures currently available, with more being released in January until Origins 2017 when the release schedule for 5e and ARPG (the PCI custom-made system for Arcanis) completely harmonize.
2) The released modules are written assuming a 4 hour timeslot, but beyond that are in no way tied to any single venue. There are no official games scheduled at game stores from a PCI level, but your FLGS may have local groups. Basically, anywhere you can sit for 3-5 hours and play a game is perfectly fine for Arcanis!
3) At present there is only a Primer released (on the same website as above under "Campaign Documents"), as well as the Campaign Guide. There are plans to release a full-fledged book similar to PCI's 3.5e Players Guide to Arcanis as well, so stay tuned for any announcements on that front.
4) Arcanis has versions of many of the 'standard' Monsters available, though some have been reskinned to fit the universe. For example, Goblins and Orcs have more or less been combined into a creature known as the Gar, and Serpent-Men are reskinned under the name Ssanu. At present for home campaigns, feel free to use whatever monsters you wish, though if you are seeking inspiration may I suggest checking out the original Codex Arcanis book. It was released for 3.0e, but it contains a large amount of data on the setting, including hints as to the types of monsters you may find. (Codex Arcanis is available from most online RPG book sources, like drivethroughrpg).
5) The 5e Arcanis setting will use much the same material as other 5e SRD sources (including the original 5e sourcebooks). The Living campaign itself will release its modules as self-contained adventures, with GM notes and directives for the narrative.
6) PCI has a longstanding tradition of allowing fans to write adventures, though PCI also reserves the right to approve what they publish in the Living Arcanis (as well as the ARPG Legends of Arcanis) campaign. All adventure pitches must be submitted for approval to pcihenry @ gmail.com (remove the spaces accordingly
) as a 1-ish paragraph pitch. If accepted, the Campaign Staff will then ask for a Scene/Encounter breakdown to expand on the idea, and if that is also approved it will move onto the first full draft (and then on to all subsequent drafts, edits, playtests, etc).
I should mention that because of the nature of the Living campaign (as opposed to a home campaign) there are reasonably strict guidelines as to what kind of adventures can be accepted , primarily because the main storyline of Arcanis follows a fairly set narrative (as written by Henry Lopez and the rest of PCI). Because of this, large world-shaping events are unlikely to be accepted. For example, if you have an adventure where the Heroes travel to Illiir's Paradise of the Gods to kill the Gods themselves, it will most likely not be accepted as it does not fit within the greater meta-narrative of the story of the campaign. However, stories such as the Heroes discovering a cult of demon-worshippers, raiding the estate of a rich collector of antiquities, etc are within the realm of the kind of stories which would be accepted (especially from a first-time author).