The Workshops are the actual buildings in those slots.
pg 12 in the rule book gives the order of events for placing in a Guild.
1. Activate Workshops (the buildings built in the Guild). You activate them whether they belong to you, someone else, or belong to no one.
2. Buy Goods This applies to the action on the specific slot where you placed your die. You do not get the board actions from previous slots. When you place a 5/6 die, you can buy up to 3 goods, but you can not place an apprentice.
3. Place Workers This action is available only with the 1/2 slot and the 3/4 slot.
Your specific questions 1. No, only in the 1/2 and 3/4 slot. 2. No, you can only use the board ability for the slot you placed your die in. 3. No, the Buy Goods action happens before the Place Workers action 4. All Workshops up to the placed die activate. You can take advantage of the ability on the tile. You do not get the ownership bonus (shown on the board above the Workshop) if you activate your own Workshop. 5. Correct.