Bergamo airport is just as easy as Verona for Lake Garda. How long depends on where exactly you are staying and how you intend to get there.

the airport's own ground transport info in English is here. The train info link takes you to a really complicated page in Italian but tucked away at the top right is an English button which makes it much simpler!

Only Desenzano and Peschiera have railway stations, Airport to one of these will take upwards of 2 hours allowing for connections.

the other resorts will require a bus connection or a hire car (and the best of luck if you choose that!!). Train fares are relatively cheap but are complicated by supplements if you use InterCity or better. Local bus fares are also cheap but can also be quite complicated and for services within a town you may have to buy the ticket before you get on.

For your other question about excursions, Venice is probably best done with an organised tour if it includes an English speaking guide because of the complexity of the journey by train. One place I would recommend if you are at the north end of the lake is Bozen (or Bolzano as they call it in Italian) which is the centre of the German speaking Sud Tirol (Alto Aldige) and home to both Otzi the Iceman and some very nice beer!

I'd also be interested in answers to this question because we'll be undertaking a similar journey in July when we go from Bergamo to Limone.

So far the best advice I've received is a coach/bus from Bergamo to Limone or the same to Desenzano, Peschiera or Sirmione and then catch a ferry but this criss-crosses the lake to each stop off. Both can take around 2 hours or more.

I'm not expecting express travel but I would like to be at the hotel before midnight.

Limone is just within the province of Brescia who do an interesting English language site here. Unfortunately some of the links don't work - most notably public transport. I've tracked the timetables down to here but only in Italian. Pick Limone from the drop down list of towns and it will give a list of routes with PDF format timetables. There is also a more complicated site from Lombardy Region here which also includes the boats, pick the option that starts Visualizza.. and then the first option and type Limone in the box.

The main bus service to Limone is from Desanzano railway station and takes about 90 minutes, it shows the Hotels L.da Vinci and Panorama as specific stops if that's any help. But note the last bus from Desanzano is at 18:30 and be aware that the note fer means workdays (inc Saturday) and fest means holidays.

There is a very limited service from Brescia bus station close to the railway station which would make the journey from the airport quicker if you were lucky enough to connect with the train. Unfortunately the direct Airport-Brescia coaches don't connect, otherwise this would have been the ideal option.