He wikid, welcome to the forum!
Good idea with the RCA-4, beautiful looking kit under any stain! Feel free to ask any questions, and as many as you so desire! Now the hardest part is waiting for the kit to arrive!

Doesn't matter of you go for a solid colour or use a stain, you want to sand the wood back to allow for the finish to come out as good as possible. One of The moderators dingobass always has the mantra of "sand, sand, sand and sand again. When you think you are done sanding, sand again! When your arms are tired, give it to your wife to sand!", always works well if you give it another half hour or so of sanding! I gave my Strat kit a whole week of just sanding and it came out beautifully!

Make sure to setup a build diary when you get the kit and we will guide you to build one awesome bass!