From here it looks like you have learnt a lot by having a go. The right tools make it easier but it is just practising to use them together with visualising what needs to be done before starting. How about finishing the tender as one of the less than pristine examples in one of the GW weed killing trains? See here - A little fun: Can we identify this tender? Buying a couple of sheets of 10 and 15 thou brass (eg. K&S) would provide materials to scratchbuild a copy or two as practice pieces at very little cost - only buy the spring castings etc if they work out as you want. If I were to scratchbuild this tender I wouldn't use an inner former, solving your (and most peoples) biggest difficulty in one go- laminating brass is not easy. Bigger can be easier, but may need more heat.