I am not saying there were no amphibious operations, that would be stupid. What I am saying there weren't any in conditions like this. Your closest example, the Gulf of Riga, doesn't really compare at all. To get close to Turku, the attacking fleet would have to pass a number of small inlets less than a kilometer across. The water is often shallow, rife with underwater skerries. In these conditions, the defender can cause a lot of trouble to the opponent even with limited forces.
Like von Adler says, a landing more north along the coast would be much more doable.
Riga had amphibious assaults in 1915 and 1917. The landings failed in 1915, and worked in 1917.
I do agree that if the Russians are given enough time to fortified, it would be extremely difficult, so 1915 is unlikely, and 1916 is not going to happen. But in 1914, the areas were unfortified. The initial landing against and unfortified Aland will be simple. Once the first regiment is ashore, and and they begin to fortify, all the arguments you make against the landing for the Swedes would now apply to the Russians.
The Swedes will likely have to make many small landings on these Islands and inlets if they are undefended. If heavily defended, the the operation will not be done.
Trains could move troops at 20 miles per hour, and up to 40 for shorter distances. By the time the Aland assault is finished, the Russians have a extra corp in the area. Or they may not move up troops, and the Swedes can make a landing. Remember the concept of the operation. It is not that two Swedish corps will march and defeat multiple Russian Armies, the concept is that the Swedes will attack until the hit heavy contact, then go on the defensive, or even make a fighting withdrawal.
Kuwait or Tanga are excellent examples of largely unopposed landings. And Riga is an example of attacks against much greater naval defenses than Finland will have at any point in 1914. Tsingtao is probably the best example. Landing 23,000 troops away from the main base of the enemy with master of the seas. Yes Sealion is impossible, and D-Day took years to prepare, but these undefended, lightly-defended coast lines have little in common with these much larger amphibious operations.
I think the plan is to take Aland and as many island towards Turku as possible and bottle the gulf of Bothnia up whit a mine belt protected by artillery batteries on the islands or ships hidden in the archipelago. Denying Russia easy sea access to Turku is much cheaper than landing troops.
I also think the plan were to wait in the forts around Boden for a Russian invasion. Fighting something of a delaying war of attrition down to Boden to bleed the Russian troops dry.
Combining this whit harassing operations along the Finish coast in the gulf of Bothnia is a good combination as the Swedish fleet would be uncontested there and the Ice generally freezes over quickly and hard enough to use as a transport rout for horse sled caravans(unsure if there is enough horses to ferry enough supplies thou). The islands along the Finish coast could also be used to bunker up supplies before any larger operations in northern Finland in 1915. This could be combined whit building a rail bridge over Tornio river and (if it seems important enough) relaying of tracks down the Finish rail lines to fit the Swedish gauge during 1915 to establish a front in Finland that could be supplied. Something I only see happening if German high command makes some rather believable arguments about the ability to knocking Russia out early 1916. Maybe combined whit the cold hand in Swedish attempts to establish a separate peace whit Russia making the Swedish war government more desperate.
If Germany follow this up whit taking Hiiumaa and Saaremaa (Dago and Osel) and bottle up the Russian fleet in the bay of Finland during 1914 and makes a amphibious landing somewhere closer to St Petersburg (best option Narva but more likely Tallinn) in 1915 this could trigger a panic in the Russian capital and forcing the Tsar to withdraw more troops than necessary from the eastern front to its defense in 1915.
I could see the Swedish political establishment go for a more active approach in Finland if it seems that there is no way out of the war and pushing Russia together whit Germany would make Russia fold. The mood in the Swedish population is for a short war but to defend Sweden against its attacker whit the means they have. A period of victories (successfully taking Aland and successful operations in the gulf of Bothnia no hard opposition from the Russian army) would make the population pushing for more daring strategies to shorten the war.
The plan is to take Aland and fortify. If Turku is not reinforce, take Turku and cut the rail line to north Finland. And then over time neutralize or take the entire coast of Bothnia. Aland makes it much harder for Russia to attack Sweden proper, and Aland is easy to defend with control of the seas.
Sweden having a corp in the Aland area will most likely cause the Russians to nearly panic, and tie up a lot of forces defending the long Finnish coast line. IMO, the likely chain of events would be something like this.
1) September 1914, Swedish Division lands and takes Aland.
2) October 1914, Russia sends a few extra corp to defend Finland, and Swedish forces on Aland area grow to a full corp. Nothing much else happens until spring besides both sides digging in and building up supplies.
3) By summer 1915, the eastern front looks little like OTL. Russia has one or two extra armies in Finland compared to OTL, and the Swedish army is in contact with the Russia Army somewhere.
