So it appears as though giving a bitizen their "dream job" will double the stock without increasing the stocking price.
- Dream Job employee will double the 1 Coin value stock
- Dream Job employees will double both the 1 Coin and 2 Coin value stocks
- Dream Job employees will double all stocks
As for the "skill level", here's what the wiki has to say.
Each Bitizen has a certain proficiency with each business category (Food, Service, Recreation, Retail, Creative) ranging from 0 to 9. Based on the skills of the employed Bitizen, a discount will be applied to the cost of restocking the items or services for that business. The discount is equal to the sum of each employee's skill level. The maximum discount is therefore 27%, the profits of which can certainly add up for high cost floors.
So basically high skill bitizens cause the cost of stocking to go down. Dream job bitizens double the stock quantity for free.
The ultimate combination is obviously all three staff members will have their dream job with a skill level of 9, but until those stars align, you would need to decide on which approach to take in your situation... Probably "Dream Job" because you're essentially getting your stock at a 50% discount instead of a 27% discount.