So I've played my fair share on TF2, and I sort of know how the item drop system works. It appears to be pretty random, but happens every seventy minutes or so if I'm not mistaken. There's a limit to how many items you can get in a week, and if your a free-to-play player you only get a limited amount of drops compared to what they class as 'premium' players who had bought the game beforehand. Anyway, but how does the Workshop come into this.  
 
This is more of an interest in how the whole thing works rather then it being a fundamental understanding to enhance my enjoyment of what is a great game. But with the workshop talented folks from the community create some pretty stunning weapons, hats and other style accessories which are then voted upon and possibly added into the game. If this is indeed how the system works, how many items have been added into TF2 from the workshop? And how often does Valve add items? I actually think it's a fantastic system, but it's always fascinated me and I'm never truly understood it. From reading some wiki related articles it seems Valve contact those who have designed an item they like and test them in-game for eventual sale on the store. Are items available on the store (through the Workshop) also offered as random drops or are only Valve made items available as random drops?  
 
Just thought I'd ask and get a better idea. Much appreciated.

Here, these pages should get help answer most of your questions.

http://wiki.teamfortress.com/wiki/Drops

http://wiki.teamfortress.com/wiki/Item_quality_distribution

http://wiki.teamfortress.com/wiki/Weapons#Weapon_availability

http://wiki.teamfortress.com/wiki/Workshop

You got the first part roughly correct. However, I don't think being free or premium determines how many drops you get in a week, just what is capable of dropping. As far as I'm aware, free players can't get cosmetics like hats or miscellaneous items to drop, only weapons. Also "premium" players are not just those who bought the game before it went free-to-play, it's also anyone who spends at least $5 in the store.

There have been a lot of workshop items added to the game. Almost all of the items that come out nowadays, except Steam promos and big update specific items like some Meet the Pyro/Pyromania update stuff, are community made. They add items fairly regularly, basically every time there's a patch for the game something was added so maybe once a week on average. They generally only add cosmetic items during these small patches though. Since those don't have stats, it doesn't really matter in terms of game balance. They save weapons for bigger updates since they gotta come up with interesting stats and test them. Community made items are available as drops too. I'm pretty sure as long as it's in the store, it can also drop except a few examples like keys.

Some great info, much appreciated.  
 
Was wondering how they added weapons to the game and how they the whole 'premium' and free-to-play players. Interesting that most weapons added to the game are community made, smart move really as there's some real impressive creations on the workshop. 
 
Thanks.