Yeah, I *really* doubt they get a base in the Kerkennah islands. Why would anyone want them sticking their noses near the chock point of the Mediterranean. Personally I doubt even Cyrenaica at least for a while is likely since the Greeks will be much more concerned about even minor gains back home.
In terms of the 1 Year War (incidentally the 1877-78 war lasted 10 months!), the Ottomans will probably not do too badly, but I could see them tending to be ground down given their debt and would guess a lower-quality army, though Greece may struggle to gain centers like Thessalonica. I think a Russian intervention is likely, both because pan-Slavism's day is starting to come and Russia had bad habit of getting jealous whenever a Balkan power did too well and started looking toward Constantinople.
I think a likely scenario is Greece gains Lesbos, Limnos, and maybe Thasos and Samothraki as well as Cyprus. Then some relatively minor gains on land that leave the line of mountains guarding Thessoliniki under Ottoman control and don't go to far into Albania. Maybe Kozani, Kastoria, Korce and their environs. Something like this:
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For the other powers, I think Serbia and Montengro gain the lands they did in 1878 OTL, plus Serbia gains left bank of Drina and a bit more around Nis (basically gets more, because its role is bigger than 1878 plus already has de jure independence). I think Bulgaria likely becomes independent as Russia's 'reward' for its part in settling things. Especially since there will inevitably be massacres of Bulgarians by Ottoman forces. However, I think it would be confined north of the Balkan Mountains, no Sofia and no Eastern Rumelia. Romania gains Dobruja. I don't think you've said what happened with Wallachia/Moldavia, but would guess they unify now if they haven't already. Maybe something like this for the peace:
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