I would think you would have more control over the inventory if you stocked a weeks supply of everything. It also depends on how many trucks you have in the field.
Inventory DOES cost money but you can make that back by being efficient. Nothing worse than having to send someone BACK to a job because the supplier backordered a few simple inexpensive items.
The supplier will constantly screw things up because they don't really care about your bottom line. Honestly, a full 80 percent of orders do not come in to my warehouse correctly and if someone doesn't deal with it, it COSTS MONEY!
If you have a really organized and knowledgeable person in charge of your materials, things could run really smoothly.
I'd be a kick ass warehouse dude, especially in a residential company where the materials were basically all the same. No one would ever miss a step....but I'm old and tired.