I think they might actually skip Loguetown or combine it's plot points with Whiskey Peak. They already had the whole "Luffy's smile is reminiscent of Roger" scene in the finale, and I can't see them just repeating that moment. They also already had the oath scene, so what else is there on Loguetown? Zoro getting his new swords and Tashigi/Smokers introduction, plus Dragon helping Luffy. All of that could easily take place on Whiskey Peak, after entering the Grand Line. The final scenes already teased Reverse Mountain, I just have a hard time seeing them going back from that to "Oh well actually, let's stop at this island before we go to the Grand Line".
Either way, even if they keep, I don't think Loguetown needs a whole episode to itself. It's super short in the manga. I think they could easily combine it with Laboon/Whiskey Peak in one episode. They will probably condense stuff and make some changes to the story anyway.
Since they don't have to also include 5 full character flashbacks, they will have a lot more time to focus on the present. Little Garden could easily be done in 1 episode - honestly, it's plot is basically "they meet giants and then they fight some BW agents". Move Mr. 5 and Miss Valentine to Little Garden, no need to have them fight the crew twice. Two episodes for Drum sounds perfect, leaving us with plenty of time for Alabasta, no matter if they have 8 or 10 episodes.
We will probably get a lot more Ace, and of course Smoker and Tashigi. Probably some cameos of Garp and Koby here and there. Not sure what they will do with Buggy, he had such an extended role in S1 that I don't really need him attacking the crew with Alvida. Maybe they will find some other way to tie him in. I also bet that we would already get Blackbeard and Shanks meeting with Whitebeard. On the other hand, that would also mean that we won't see most of these characters for a long while, which might feel a bit weird.
Anyway S2 focusing on the Alabasta saga feels like a very logical choice to me and fits the length of a season nicely.
Now Season 3 is where things would start to become tricky. I don't think it would be a good idea to skip Skypiea completely but I have to agree that the arc just doesn't need a whole 8-10 episodes to itself, even including Jaya. After the characters enter Upper Yard, it's basically two volumes of fighting. I'd say one episode of introducing us to the Skypiea characters and exploring Angel Island, one episode for all of the stuff on Upper Yard, one episode for the fight against Enel, the flashback, and the end of the arc. I just don't see how that can be stretched to a full season.
My idea for S3 always was to have the first half focus on Skypiea and the second half on the confrontation with Aokiji and Water 7, ending on a cliffhanger in which Usopp and Robin have left the crew. Not sure if they would want to go that route, but it be pretty dramatic. No idea what kind of side character storylines they could do for this season though, most of the secondary cast really just disappears between Jaya and Post-Enies Lobby lol. I don't think that is gonna fly in the LA show.
Going with that plan, Season 4 would be similarly divided into two halves: first half Enies Lobby, second half Thriller Bark and Sabaody, ending on the cliffhanger of the crew being separated.
Season 5 is then pretty easy again, it would start with Amazon Lilly and show the whole Marineford saga. We would probably get a lot more scenes of what the other Strawhats are doing in the meantime as secondary plot lines.
So, 5 seasons for Pre-TS One Piece seems pretty reasonable to me.
Then Season 6, depends. They could shorten Fishman Island and Punk Hazard to two episodes each I think...in that case, I think they could do Fishman Island, Punk Hazard and Dressrosa all in one season. Or I guesse Season 6 Fishman Island and Punk Hazard, Season 7 Dressrosa? I know Dressrosa is long and bloated, but a whole season on it seems a bit much. Punk Hazard and Dressrosa would fit well thematically into one season (2-3 episodes Punk Hazard, rest Dressrosa sounds pretty good) but I can't see them just excluding Fishman Island completely.
Either way, Season 7/8 would be Zou/Whole Cake Island and Season 8/9 Wano. Depending how long the current final saga will be, a 10 season show to cover the whole series actually sounds kinda feasible! Obviously, it's much harder to predict the later seasons since we don't know what changes they will make. For example, Post-Enies Lobby will be pretty different now that we already got the Garp reveal much earlier.
