Your ebony looks extremely dense - much more so than the stuff that is commercially available nowadays, so if it were mine, I wouldn't bother trying to put a chemical finish onto it at the end. Just sand and buff to a high degree, then perhaps some Microcrystalline or carnauba over the top to keep the fingerprints off. Things like CA or chemical lacquers might look great to start with, but they won't integrate with your ebony and will chip, peel off or develop air pockets between it and the wood quite quickly once the pen is in use.