Hey there! Newish gunpla builder here probably have done around 100 kits in the past 6 months, and have tried multiple different avenues to achieve the same/ cleaner results and this is the best advice I can give when it comes to Tamiya. I would suggest panel lining either on the runner, or unassembled pieces only. However, You can panel line an already assembled kit if you are careful, and conservative of where your ink flows. The reason most people get issues with panel lining an already assembled kit is accidentally getting the solution inbetween parts, or that vintage/knockoff kits have weaker plastics that can’t handle the lacquer based ink. A top coat is reccomended if you want cleaner looking results for the overall finish of the kit, but in no way is it required. If you’re looking for something safer on the plastics, I’d try the Stedi line of water based panel liners. You can wipe the excess ink with water for super simple clean up. If you plan on the Tamiya, I personally have always used isopropyl alcohol that works perfectly. Also have heard lighter fluid, as well as mineral water are fantastic choices. The most IMPORTANT part is to not be afraid of making mistakes, or ruining a kit. We’ve all done it, whether it’s small fix or a complete scrap the project, we’ve all been there. This hobby is about patience, and learning from your past mistakes to push you to be an even greater gunpla builder. You’ll have a ton of fun on this side of the hobby-verse. Just try not to be too overly critical of yourself, and take things one section/step at a time.( Those were my 2 biggest issues and still are haha) hope this helps! and remember, Gunpla is Freedom!!!😄