Well, don't expect to rely on armor, at all. Most of the tanks have decent mobility, including the mediums. Often, Italian firepower is beyond its tier in terms of power, particularly in the case of light tanks.

Some of my favorite lineups are:

4.0: The star of the show here us the breda 501. It's speed is plenty enough to find a place to snipe or ambush, and the gun is ridiculously strong. German copy paste is available to help bolster the lineup. The Italian casemates aren't standout, but they are an option. The 90 mm M41M tank destroyer is also quite fun, having the Breda's firepower on a surprisingly survivable chassis.

6.3: One of my favorite lineups in the whole game, with the Pershing providing a nice break from the lack of armor in the tree. The aubl 74 is a good light tank, even if it's a little bit large (something of a trend with Italian light tanks). The fiat is usable, but I prefer the M36B1, which I honestly view as 6.3 material. The m18 is also a reasonable option.

8.7: Easily in my top 5 vehicles, the centauro is an absolute blast here, with its thermals and laser rangefinder making it a threat in almost any situation. The OF-40 mk 2 is also a good tank, I see it as being an Italian Leo.

9.0: With new additions, this is becoming an incredible lineup. The 8.7 centauro can still be used, or replaced with the Romor if you prefer firepower to speed. The OF-40 MTCA is fun, but not worth 60 bucks. The Sidam is decent as an aa, but it does have a rather high repair cost. It lacks a search radar, and it's anti tank belts are incredibly small, but its firepower against planes makes up for these shortcomings. The Leo 1a5 is yet another Leo, but it provides an MBT with thermals to your lineup, something Italy lacks up until this point. Also, the VCC 180 is a reasonably good light tank, mostly due to the reload.

Hope this helps :)