Is it easy to lost a title? That highly depends on how much work you do to secure it.

• Recruit people to help you secure your position as Count.
• Get to know your neighbors before the game start. Build a relationship. So that they won't try to invade you.

If you lose your title, you will lose your lands and manor. You may or may not keep your pets/items/etc, depending on whether the invader that took your title also decides to raid your house and take all of your stuff.

Everyone is taking risks by being a noble. Although there are undoubtedly many advantages as well. Just try to minimize the risk by taking actions to secure your position.

It's not possible to lose it before exposition, but if you're really a fuckup, it's possible to immediately lose it then, if the rest of your duchy/kingdom decides to ides-of-march your ass.

shaddy was pretty accurate but not totally, you'll lose all county-owned land, but losing your county doesn't mean you lose your settlement and even losing your settlement doesn't mean losing everything, you don't lose your privately owned land, you only lose it if the new noble decides to evict you by adverse possessing everything, that will be seen as tyrannical and I don't suggest it cause the count might have had friends in surrounding counties, and inside the county, and being all dictator like might scare them into backing him again.