So, dirt bikers out there: What do I need? What don't I need? Any brands to avoid? Anything to look out for? Anything not worth cheaping out on, because I'll just end up buying the better version within a month anyway, so may as well buy it up front?
Helmet:
I see dirt bike helmets are different and cheaper than road helmets. The different shape is to deflect branches? Can I make do with my road helmet, or will I get my head flushed down the loo by all the cool dirt kids if I show up in my Shoei?
Goggles:
I guess this is necessary (if I have a dirt bike lid), since everyone has them... Do I need them if I'm always out in front?

Jersey:
What's with this? Why not just wear a long-sleeve shirt??? They don't look protective at all. I don't get it. Please explain

Pants:
Do they have armour in them?
Boots:
How are these different from SIDIs? Can I get away with using my SIDIs for a while, or are dirt-specific boots necessary?
Gloves:
Yeah, they're cheap. I'll just get a pair. No need to explain
Protective gear:
What is there? I haven't seen anyone dirt riding in full leathers, but what is going to save me when I go airborne into a tree, or tumbling down Disco's little hill?

I've seen some knee protection - is it always separate, or is it often included in the pants?
I've seen some upper body armour that resembles acartoon action figures - does this go over or under the jersey?
What else don't I have any idea about?
Do dirt bikers wear skins too?