It depends what you mean by a project. I might do one kit at a time, or 2 or 3 kits at the same time, but they will all be related in some way. For example -
The old & new Airfix Defiant kits, using surplus alternative parts & patterns from the new kit to improve the old
The same types, such as Hurricanes or Mosquitoes, so I can slightly cross - kit with propellers, decals, weapons and so on, especially if they have similar colour schemes
Different types, such as Beaufighter & Mosquito, which tend to have similar weapons and colour schemes
So, there may be a few kits that are made at the same time, but I would class that as one project
I would never have totally different types on the go together, such as a Spitfire and an F - 100 Super Sabre or have, say, a plane and a ship being made at the same time.
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