Mike
We (2 adults) spent about 5 weeks in Italy all of it around the lakes from Maggiore to Garda. The autostrade are fine and not that expensive in respect of tolls. They can be busy at rush hour and round the large cities like Milan. The toll from the Austrian border to Rovereto (turn off for the north of Lake Garda) is only €13 for about 100 miles, from Austria border to Venice €30 for about 250 miles. The roads around the lakes are narrow and overtaking is virtually impossible but if on holidays you don't need to race anyway. The main national roads are generally busy and you'll be lucky to average 30mph as there are many towns and villages to go through. I think the autostrade are well worth the cost.
Fuel is much more expensive than in Austria, France or Switzerland, also many service stations charge a service fee of up to €0.20 per litre if the attendant fills for you. Make sure you fill up before you cross into Italy. We paid €1.55 in Italy compared to €1.20 in France, €1.25 in Austria and €1.20 in Germany last summer, it is a bit cheaper now.
We found that around Lake Garda there are quite a few dedicated motorhome parking places where you can also overnight but the quality is not great; OK for an en route stop. Many of them do not have any facilities, those that do are barely useable. They cost anything from €10 to in excess of €20 per night.
Depending on when you travel (peak season starts in early July) and potentially using ASCI a site with full facilities will cost little more. The sites do however get full at weekends.
We did find two superb Aires both in Peschiera which I think are owned by the same people. They had full facilities - EHU, fresh water, grey and black water dump for €15 per night or €5 for a few hours to allow you to dump and replenish. Also showers at €1 each. They both hold about 100 MH, one is close (5 minute walk) to the town centre, the other about 3 miles out. The one close to the town centre is on a bus route to Verona and Gardaland or a mile walk to the Milan to Venice rail station.
The Aire in Peschiera town is at N45.43979, E10.68468. Google "Peschiera motorhome Aire". Payment CASH only into a carpark type pay machine. All gravel hard standing on a slight slope.
The site at Innsbruck is Camping Judenstein at N47.26002, E11.50516 is located near the village of Rinn about 6 or 7 mile outside Innsbruck. Cost was €18 incl EHU per night. Google "camping Judenstein Rinn". Pay warden who visits for a couple of hours night and morning. All grass pitches.
You can travel toll free the whole way from Calais to the Austrian/Italian border and apart from the stretch across Austria it is virtually all on motorway or main trunk routes.