Every list-attempt just shows the futility of over-reach in 11.5 days. First, you can only count arrival day as 1/2 IF your plane arrives nonstop at 9:15 or 9:30 AM (which I very much doubt on a bargain flight) & you can't count Departure day at all. So it may be just 11 days. I advise on basis of 13 trips since 1999, 10 of them with newcomers like you along. The reality is, each move will cost you at LEAST half a day... if you believe you can just magically zip from one to another, you must be thinking of Star Trek and 'Beam me up Scottie". The first list made me gasp --- Corfu to Rhodes!!! Aaaach! Even your 2nd list is somewhat of a fantasy. Please, look at maps, check ferry skeds and domestic air (Aegean/Olympic), don't just look at eye candy on your phone... lets make this trip both wonderful AND do-able. The secrets to success: cut islands to 3, workable sequence, figure out transport, & apportion time realistically.. Example: Santorini is 12 miles long. Crete is a COUNTRY --- 170 miles! Allot accordingly.
Since Hiking is your thing, and crete's great for it, consider this:
DAY 1 - immediately upon landing, ASAP (allow 2 hours for switchover) board Flight to CHANIA, CRETE.
Day 2 - Explore gorgeous CHANIA, 2nd most beautiful Old Town in Greece ... book 1-2 of numerous good West Crete hiking or "jeep safari" adventures in the hills, mountains (If you want to do a Gorge, book IMBROS, do-able in 2 hours - the Samaria often is not open in april, and anyway would take 7-8 hours & require a recovery day that your short-short schedule doesn't permit).
Day 3 & 4 - Those adventures
Day 5 - get up at dawn, take KTEL 6 am bus to get to Heraklion for 9:45 ferry to SANTORINI (arrive noon). Stay in FIrostephani, devote afternoon to enjoying view, walking along rim to Fira Town, enjoy sunset from a high terrace restaurant, NOT in Oia.
Day 6 - Take 8:30 bus to OIA, to enjoy & take pix before cruise ship mobs invade and clog all lanes to impassability. at 10:30 or so scram outa Oia, and find somewhere else -- bus to Akrotiri (excavation or beach), or to Pyrgos, a town tourists bypass... findyour own sunset place NOT in Oia ... that's where the lemmings go, even in April - take a look at this montage of jampack throngs struggling along the Oia rim, scenes NOT shown on your I-phone: http://tinyurl.com/lnquk6h
Day 7 - Take 10:45 CHAMPIONJET ferry to Naxos (arrive about noon) -- book hotel in St. George (Ag Giorgios) beach directly adjacent to port town (other areas won't be "open" yet). Afternoon; explore fascinating Old Town, winding mazy paths to Kastro atop town -- out on Causeway at dusk to photo sunset thru the famout arch.
Day 8 - 9 - Bus or taxi to Naxos mountain villages to hike among beautiful spring flowers & greenery, see villages & farms (we once watched a farmer shering sheep in his field in early May). This website suggests good hikes: http://www.cycladen.be/NaxosEng.htm - here are typical scenes around island -- http://www.flickr.com/photos/stanbr54/sets/72157634605629689/
Day 10 - a final AM in Naxos, then fly ATH, taxi to Plaka-area hotel. Rooms in Chania, Firostephani, Naxos in April will be bargains (40 - 50€ per night). So I suggest minor splurge in Athens, on South Side of Acropolis, by Acropolis Museum & the lovely pedestrian promenade along that side -- Hotel Herodion. Has a super roof-top estaurant w. Acropolis view for final-night dinner; upper-floor rooms have Acropolis-view balconies... and I've heard that when you book (write an e-mail, don't just fill out a form), if you say it's your honeymoon, and add flattery how their hotel can make your Greece dream trip complete -- you may score one of the best rooms, and perhaps a celebratory bottle of fizz, as well.
DAY 11 & 12 -- Experience the stunning landmarks & museums of Athens, all of which will mean MUCH more to you at the end of 10 days of immersion in Greece landscapes, legends and culture.