Is it time to buy a jointer?

Greetings all, I have a hopefully-quick plane question:

I'm looking at upcoming projects and fairly high on the list is a new desk for my office. My goal will be to make it from planks - no plywood - so I'll need to attach several long boards in order to make the table top. Making this tabletop will be one of several big "upskills" I have in mind for this build since I haven't made any big panels before and this is an application where some flaws won't be the end of the world.

I don't currently own a jointer plane. I have a block plane, a #4, and a #5 (all Stanley). What's the general opinion on jointing a board approx 6 feet long with a #5? Obviously it's doable with enough time and a really good straightedge to check it, but I'm thinking a jointer would be a good investment for this job. I'm thinking a #7 - doesn't need to be Stanley, I'd be happy with a millers falls, union, sargeant, or a couple others that escape me at the moment. The #8 looks appealing from a "biggest and flattest board" standpoint, but the drawbacks seem to be a bit much considering I'm not doing any jointing yet.

Am I crazy for wanting to get a jointer just for this job? It just feels like it's the best tool to do what I need for this desk.

Thanks!