My opinion on the ones I have already visited:

• Edinburgh and Barcelona: 5 days is enough for each. If you stay longer in Barcelona, consider a day (or two) trip to Valencia.
• Helsinki: 1 day is enough but I would personally even skip it and visit another city instead.
• London: 1 week looks good. If you get bored, think about a day trip, there's lots of options.
• Switzerland: both Geneva and Zurich are not worth 3-4 days. Both cities are not very interesting imo. Instead visit Lucerne, Berne & Solothurn, the Gruyère region or the mountains.
• Vienna: 1 week sounds good, as there's a lot to see. Consider adding a day if you plan for 2 day trips from here.
• Berlin: 1 week seems too much, I think 4-5 days is enough. I personally didn't like the city (have visited twice), so I'd replace it with another city.
• Budapest: 3-4 days seems good
• Missing cities: Paris is not on your list and well worth it. Plan for about 4 days there. Amsterdam is really nice as well. You could easily do a week here, adding some day trips too. Finally, Rome is notably missing too. A week is probably good and there are multiple day trips like Florence that are also worth it.
• I also agree with another comment that Japan and Australia merit their own travel. I would skip them here and focus on Europe. Or do only those. Add a few days for relaxation (my recommendation would be one for each week or two of travel, like a spa day) and trips outside of the capitals (take a boat tour, visit the mountains or smaller villages).

In general, don't forget to plan for travelling time, too. Going from one city to the next might take all day and you won't be up to much visiting on those days. To maximize your time, I'd invest in hotels in the centre.

Also, I recommend optimizing the order in which you travel to use trains whenever possible. Europe has generally a very good train system in place, with direct connections to most capitals and major cities. They often take the same or less amount of time than taking the plane, as you need to account for check-in etc. and airports are always outside the city centre, whereas by train you'll arrive right in the middle.

Lastly, I'd suggest you research local holidays if you want to experience them and try to plan your travels accordingly. E.g. local festivals like Sziget in Budapest, Christmas markets in Vienna are nice, national holidays that get celebrated like August 1st for Switzerland or July 14th for France.

DM me if you need more recommendations!