Hi Michele
Yes, twice. The first time as part of a 2 week holiday taking in Bologna, Verona and Molveno. That encouraged us to have a more focused holiday split between Trento and Molveno, with just short of a week in each.
Getting there is one of the challenges, as there isn't an international airport. However both Bologna and Verona are good options to fly into, with regular fast ES* services, and on the 2nd trip we had enough time to pick up a little food in Bologna before catching the train.
There are other options as well, e.g. Treviso, or even Austria, and it can depend on what flights you can get.
How long should you spend there? As long as you want. Plenty to see and do, but we did like the combo of Trento (a very charming city with wide pedestrianised streets) and being in easy reach of the mountains for walking.
If you choose Trento, there's a good weekly street market, so worth aligning with that - ideally on 1st or 2nd day there, so you can stock up.
The food definitely straddles the Austro-Italian border, and whilst we did encounter one person who flatly refused to speak Italian, generally it's Italian leaning. I understand Alto-Adige / Sudtirol leans the other way.
Personal highlights? Foradori for a winery visit, in a suburb of Trento (Mezzolombardo IIRC), walking and cable car trips in the mountains, a super resturaurant in Trento that I believe closed not long afterwards, mushroom hunting (though it was dry, so not much to pick), visiting cartoonist Fabio Vettori in a Trento suburb (his speciality is formiche, ants, in landscapes), the mad butcher of Trento - such a wonderful energy in a delightfully exuberant / unhinged way), La Bottega Delle Bontà in Andalo - a super specialist food shop, the stunning views in Molveno - no boring filler here, the old cable car running from behind Trento's train station - it has real charm and the cost was negligible.