Short answers, pulled from the story.
Matthew Boulton and James Watt signed a formal agreement in 1775 to commercialize the separate condenser patent. This partnership formed the core of what would become a major British engineering firm.
The Soho Manufactory served as the initial base for all engine assembly activities starting in 1775. Components arrived from external sources like John Wilkinson who crafted the large cylinders needed for operation.
Boulton and Watt opened a dedicated facility called the Soho Foundry in Smethwick in 1795. This move marked a shift toward making steam engines entirely within their own walls.
Charlotte Matthews served as the primary banker for Boulton and Watt from 1792 until her death in 1802. Her financial support allowed the engineering firm to grow beyond its initial capacity during the late eighteenth century.
Final production ceased when W & T Avery Ltd purchased the business in 1895. The firm continued operations for over 120 years under various names including James Watt & Co which appeared in 1849.