42 Nights in 2023, Multi JR Pass or other?

I arrive in Japan in March 2023, for 42 nights.
I've booked up to six nights accommodation in each of the following places; Yokohama (to commute to Tokyo & visit Hakone), Matsumoto, Kanazawa, Kyoto (Nara day trip), Takamatsu (Shikoku & Inland Sea Islands), Hiroshima (this takes me up to 12/4/23).
I then want to stay in Kyushu for up to five nights, before taking overnight ferry from Kagoshima to Okinawa. I have accommodation booked in Okinawa for six nights before flying back to UK, just before Golden Week.
Here's what I'd like to know, please:
1. May I buy more than one JR Pass before departure? One for the first 14 days of my trip, then another to run for the next 21 days of my trip? I don't think I'll need a JR pass for the last week, when I plan to sit on the beach!
2. Are there other travel pass options that you would recommend?
3. I have been trying to book the overnight ferry from Kagoshima to Naha. Marix Line website switches to Japanese when I click through to "Timetable & Fare" or "Reservation & Boarding", whilst A Line website seems to say I can only book 30 days in advance. I'm happy to ask for help to book the ferry once I arrive in Japan, but thought I'd ask here, in-case anyone can advise me how to book online from UK before departure.
Thank you for reading my post & I look forward to reading your informed answers!

1. Yes, you can buy as many JR Passes as you want. But see 2 below.
2. With your itinerary, you may want to consider more regional passes. Like:
https://www.westjr.co.jp/global/en/ticket/pass/
http://www.jrkyushu.co.jp/english/railpass/railpass.html

Six nights in each place would mean the national pass would be quite unlikely to offer much in the way of savings. (and would probably cost a lot more than single tickets) The national passes are good if you are doing a lot of long distance travel on multiple days, and you are not doing that. But, yes, you can buy multiple passes and use them consecutively.
As for the ferry, many transport options only allow booking one month in advance - like the trains.