About plausibility, by all means, the first option (Russo-German-Italian) is the most likely since it requires the less radical PoD. A strong interest in Russian friendship was one of the OTL cornerstones of Bismarck foreign policy, as the OP indicated, the PoD only requires that Bismarck has an extra bit of insight during the 1870s about the weakness of A-H and the necessity to pick a strong ally in either Russia or UK.
So he decisively sides with Russia during the Berlin Conference. This leads to the birth of Greater Bulgaria (with Eastern Rumelia and Vardar Macedonia) and the expansion of Greece (with southern Epirus, Thessaly, and Aegean Macedonia) as Russo-German satellites, and resentful A-H turns to France for an alliance. Albania may become an Italian protectorate. A-H most likely gets protectorate over Bosnia as a consolation prize. Serbia, resentful for the missed gain of Macedonia, reluctantly turns to A-H and becomes its satellite. Italy strenghtens its old ties to Germany into a permanent alliance and so does a grateful Russia. The Triple Alliance (Russo-German-Italian) takes shape during the early-mid 1880s. Secret plans for the partition of the Habsburg and Ottoman Empires by the Triple Alliance in case of a general war are drawn.
The Ottoman Empire, alarmed by the outcome of the Conference, and the Russo-German alliance, joins the Austro-French Entente. At the turn of the century, Britain, faced with growing strategic rivalry with Russia in Central Asia and the Far East, and naval rivalry with Germany, buries old naval rivalry and colonial competition with France , and enters the Triple Entente. Romania may become another satellite of the Triple Alliance, out of greed for some slice of Transylvania.
Now, this Triple Alliance could have rather interesting results if the Allies support Russia during the Russo-Japanese war. The Transiberian Railway could hardly support supplying more troops than OTL, so a German-Italian Expeditionary Corps is rather unplausible. OTOH, if Germany and Italy send a fleet to support Russia and they arrive in time to fight at Port Arthur (a big IF), this could lead to a Russian victory in the war, or at least a draw. OTOH, this might easily lead to a British intervention in the war, so maybe Germany and Italy doen't intervene and the war has its course pretty much like OTL, or allthre powers do and WWI occurs in 1905.
If the Russo-Japanese war is not the trigger point for Alt-WWI, other possible ones might be Italian-Ottoman clash over Tripolitania, German-French clash over Morocco, or renewed hostilities between Serbia and Bulgaria over Vardar Macedonia, or something else entirely (e.g. Russo-British clash over Persia or Afghanistan). It is most certain, however, that the Balkan Wars would be entirely butterflied away since the partition of the European Turkish possessions would have already happened.
On land, this Triple Alliance would be quite powerful, since Germany and Italy would go on the defensive on the Western Front, while the Anglo-French bleed themselves to no avail in Alsace-Lorraine and the Alps. The Entente might or might not violate Belgian neutrality. Belgium would most likely resist and call for German help, and the Dutch would intervene for the Alliance, causing the Entente offensive to stalemate on the Meuse. In the meanwhile, combined Russo-German-Italian pressure, with the support of Bulgaria, Romania, and Greece, gradually crush A-H in a deadly vise over six months to a year. Britain and Russia clash ineffectually in Persia and Afghanistan. Serbia manages to survive as long as A-H does, since Bulgaria and Greece fight a two-front war with the Ottomans. Afterwards, they are swiftly encircled and destroyed. The Ottomans are able (with the likely help of a British expeditionary corps) to stalemate the Russians in the Caucasus, but after A-H and Serbia are vanquished, an overwhelming number of Allied armies converge on Constantinople and after a savage trench warfare carnage in eastern Thrace, occupy the city and knock the Ottomans out of the war.
On the naval theater, the German and Italian colonies are soon lost, as the RN and the French Navy bottle the HSF, the Russian Baltic/Black Sea Fleets and the Italian Fleet in their ports. Italy and Greece feel some serious economic hardship in the first months of the war, as the Anglo-French blockade them and maybe land to invade Crete or Sardinia. A landing in Sicily would most likely be TTL equivalent of Gallipoli. But in all likelihood, very soon Germans and Italians reestablish a land connection through Tyrol and German-Russian commodities relieve Italian economy (for the same reason, Germany does not suffer the blockade as harshly as IOTL, thanks to unlimited access to Russian foodstuffs from the start).
After A-H and Turkey are knocked out of the war, the vast majority of German-Italian forces, and a massive Russian expeditionary corps, attack France on two fronts and achieve a strategic breakthrough after several months or brutal trench-warfare struggle through sheer force of numbers. Britain, seeing the writing on the wall, after some months, bargains integrity of its pre-war Empire with acknowledgement of the Alliance's continental supremacy. Hmm, say a couple years from beginning to end.
As it concerns the peace settlement, as before, Britain would most likely gain a white peace, maybe with some minor colonial concessions in Central Asia and Africa, and must return German and Italian colonies. France is forced to cede Lorraine, Morocco, and French Equatorial Africa to Germany, Nice, Savoy, Corsica, Tunis, and Djibouti to Italy. It may or may not keep Algeria (likely partitioned between Germany and Italy if lost). The Hapsburg Empire vanishes off the map, with Germany annexing Austria, Bohemia and Slovenia, Italy annexing Trento, Kustenland, Dalmatia, Russia annexing Galicia, Ruthenia, and Bukovina. Hungary becomes a Russo-German satellite, and it would most likely keep Slovakia. Since Serbia was a defeated enemy, the Allies have no interest in aggrandizing it. So Croatia may stay an Hungarian possession as well. Romania surely gains southern Transylvania, northern Transylvania might go as well or stay with Hungary. Bulgaria gets eastern Thrace, minus the Straits themselves that go to Russia. Greece gains Cyprus and western Anatolia. Italy gains a protectorate over southern Anatolia. Russia annexes northeastern Anatolia and northern Persia and establishes a protectorate over southern Persia, Afghanistan, and northwestern Anatolia). Germany gains a protectorate over Syria and Iraq-Kuwait. Italy gains Libya.
Japan would honor its British allaince and attack Russia, making some serious inroads in Manchuria and Eastern Siberia, but being eventually forced to sign a compromise peace with Britain does so. It is surely forced to cede Manchuria to Russia, but it may keep Korea. Indochina most likely goes to Germany.
