Paigetrain, there were a few things mentioned in your opening post that caught my attention.
- going into business with your grandfather. How is his health and physical capacity to support this business in the longterm.
- it seems your parents are somewhat opposed to your interest in trains as a hobby (observation from your past posts). Opening a train business would certainly be easier with some or total buy in from your parents.
- you've listed building a layout as the first benefit and the chance to possibly make money as a second benefit. If you don't have a solid business plan to make a lot of money (high percentage profit), I would be very concerned. Unexpected problems are certain to decrease your planned profits, such as covid, supply chain, or a financial recession. The toy train hobby has seen several experienced, previously profitable hobby shops close in high numbers over the past ten years. I would concentrate on understanding why those shops closed and what you will be doing differently to avoid those problems.
- I would suggest watching some reality shows about start up businesses like Shark Tank or The Profit. Learn from the criticisms that the "experts" are expressing and the weaknesses they see.
-I didn't see anything in your post about plans for repair and service after the sale. You will probably need to address that aspect as a prime factor in your business.
As mentioned above you will need lots of money and of course expert advice from Mike.
