1. Do set your receipt to be 2 steps, to enable quality check of bought products.

2. Not certain the need for BOMs as the manufactured products are being bought. BOMs can be created from product page or from Manufacturing app. Since there are subassemblies they would require to be defined as products and then associated boms.

Variants can included in a single BOM (by utilizing apply on variants field on BOM lines) or a separate BOM can be created for each variant.

3. Ensure the routes that are applied to manufactured products is ‘buy’ so the reordering rule doesn’t create a manufacturing order.

4. Would recommend the use of repairs app which has would consume or increment the components used or changed.

In this business flow don’t seem to see the use of BOMs any more than just documentation.

Hope this address your question 

By creating more than one warehouse. You mean to create a warehouse for selling products and one for the spare parts used for repairs, right ?

To address the scenario please create separate warehouses, by  utilizing Odoo's routes and rules you can achieve the functionality.