RE: Item Locations Bins/Shelf - Inventory/Warehouse Management
You could simplify some of your processing here.
For the 3PL Warehouse. If you don't manage the physical movement, placement, and picking of product, then you don't need to know the Item's exact location in the 3PL's warehouse. Hopefully they are tracking the specifics of the product. You would only need to track that product was received and eventually shipped (transferred) to your store Location. This means you can leave everything off for this Location. You will still receive and ship (transfer) out of that Location, but you won't be doing picks, put-aways, etc. to specific Bins. The 3PL's system will be tracking that level of detail.
For the Showroom/Storage Room, you could make that a single Location. The Bin Codes can make it clear whether it is a Showroom (SH-01) or Storage (ST-01) bin. This avoids having to do a transfer order for the product to move from Storage to Showroom. Also, if someone needs to pull from the Storage area to fill a client's request, they are only changing the Bin Code on the transaction rather than processing a full Transfer between Locations.
The downside to this method is you don't get to control inventory level by Bin, only by Location. If the Showroom sells out, there won't be anything to tell you to move product from Storage to Showroom. Depending on what you sell this may or may not be a big deal. In the previous scenario where you sold something out of Storage, you could also change the Location on the Transaction to pull from Storage.
You should discuss this with your Business Central partner to get their input. Obviously there are a lot of options and flexibility within the system. Either way you go, be sure to use SKU's per Location, it gives you a lot more flexibility with the MRP calculations.