The naval aspect of the game is very tricky because naval battles can be very decisive. And a small mistake (like allowing damaged ships to detach from the main task force) can in one instance wipe out "years" of preparation. Italy is particularly unforgiving since they need to keep their own in the mediterranean while facing superior opponents, so at least avoid the temptation naval combat until France surrenders and their fleet is gone!
In general, I would not clear the queue. The "discounted" ships in construction are always going to be useful! If you just want to get some practice, why don't you load up the 1939 scenario? And for practicing upgrades, the US is a good choice. It does not have a lot of command points for naval advisors early on, but you have infinite oil for naval exercises.
One thing to keep in mind as Italy is that your fleet will often operate in range of land-based aircraft, so light AA is a priority. Torpedoes are good on fast ships - and you will need some destroyers with sonar. Don't be afraid to leave slots open for later upgrades (DP light guns, for instance). Look at the cost and actual stat increase from each upgrade to see if it makes sense for you, or if the shipyards can be better spent on something else.
In terms of doctrines, fleet-in-being is probably the best overall. Trade interdiction only makes sense if you think that you can take control of both Suez and Gibraltar go for a submarine blockade of Britain.
On another note, light armor is a lot of fun in China. You can send two divisions to help Japan (along with some CAS once you take Beijing airport).
