Belgium Citizenship by marriage.

Hello,
I'm a US citizen currently living in the US. I was born here and have lived here my whole life. I'm engaged to someone who is a dual citizen in the US and in Belgium. They were born in Belgium to one Belgian and one American parent. They have lived here for years, but want to move back to Belgium. That sounds great to me, too! So, what is the best way to do this? Many options, and many questions!

Our current plan is to be married here in the US in January. Then, move to Belgium together. However, I'm not sure if that's the best option. First of all, they haven't lived in Belgium since they were under 18. But they can still hop of the plane and get a job and rent an apartment and register to vote and everything, right? They don't need to do anything to be allowed to work, reside, etc?

Secondly, can I apply for a visa simply for being married to them...? Like, do I need to have any other reason to be there? Please also consider that my spouse will have not lived in Belgium since they were a teen, so factor that in, in case it affects their ability to be my reason for applying for a visa. All of the info I could find about this sort of thing were Americans who wanted to go to Belgium and then marry a citizen while they were there. But if I'm already married to a Belgian citizen, what do I do...?

OR, is there no info on this because being married to someone doesn't count for crap? If so, would it be better to have a wedding here but not *actually* get married (ie a party with no license) and THEN move over there, and do a courthouse gig? Because we're fine with that, too. We want to do whatever is easiest.