Tripod masts intimidated me, too. The keys are to sand the platforms until you can easily peel the flash from the wafer away, then dry fit. It's important to get the decks as close to the thickness that was originally cast to avoid getting the complete assembly too tall, which throws off the angles of the rear legs.
It helps to use a dab of white glue between the levels so you can slip them around until you get them aligned, then use a toothpick at apply CA glue to the seams. I also use a small round file to align the holes for the rear legs. Of course you can also separate the levels and wash off the white glue before final assembly, but the height will be about the same and you'll have to align them again.
Set the vertical mast first, then measure the length you need for the rear mast using a pair of dividers. The length can't be measured off the plans because the length depends on both the fore and aft angle, but also the side to side angles. It's easier for me to cut the rear legs slightly longer, make a pencil line level with the vertical leg, nip them close to the line with a fingernail clip and use a sanding stick to make final adjustments.
I know that a lot of people have replaced the plastic tripod legs with brass, but as long as you are careful about aligning the holes, plastic rod is as straight as brass and strong enough. I have lifted a nearly completed model by the fore top without damage.
I made these things for people to have fun building them, so even if you mess it up, I have free replacement parts so you can try again.
I'll keep making them as long as they are viable and I have new ones in progress, so I still have hope.