Hi RaaArtyGunner,
there are a number of things to watch out for on the yamato, the first and worst problem is if you have one of the last kits to come off the productoin line you will find as i did with mine is that the hull sides were warped inwards so the fitting of the deck was very hard, and the second problem is the parts have very bad flack on them and are hard to clean off without breaking the parts. If you are going to fit running gear in it then DO NOT USE THE PROPS AND SHAFTS that come with the kit as they are shite. i got the prop shop to make some up for me and had shafts made too, cost me a fortune but it was worth it, also before starting to build i would recomend buying the brass etching kit, i didnt and regretted it. ballast, well basically you need a hell of a lot to bring it down to the waterline i used 4 18volt drill batteries wich just about got it down enough.
Now the S-100 was a dream to build all the parts are clean and went together too well and basically it only took me about 2 weeks to build and get in the water, now the running gear i used was just 2 props and shafts with 3 rudders, motors i used were 400s and a 6v 4.5ah lead acid battery giving me about 40 mins of run time and cuts thru the water amazingly well for a plastic kit. shg recomends that you use 3 props and shafts but this is not true and runs fine on just 2 which i think is the true scale speed. ill try and send you an email with the quotation i got from them in a bit hope this all helps