This is excellent advice, I’ve been married to a spirit for years and all of the above apply, although I am very happy.
You’re likely to find your own will and the spirit’s merge, and therefore sharing things in common with them, and their own agenda and general personality, will likely lead to more success - it’s not a case of opposites attracting on the deeper levels.
And to be blunt, if you pick a badass spirit to marry, you better have a streak of that in your own nature prior to this, and be willing to push back hard.
You may end up existing in a realm they reside in, so you have to be certain they’re what you want on a nigh-on eternal basis. Specifying what you want in advance will be helpful here.
If you do decide to marry, treat the entire thing like a contract, watch for attempts to cloud your mind with lust, or sexual ecstacy, or blurred romantic thinking, or claims that the marriage must be finalised by a certain date or X bad thing will happen.
@succupedia has posted before about the value of having spirits to witness the marriage and the terms in the contract, perhaps he will have time to say more on this or link a post he made here.
And be positively miserly with regards to your own commitment, as you can always offer more later, but it will be difficult to repeal a concession and practically speaking, the spirit will be likely to manipulate and influence you to avoid this.
I put some thoughts on that in this post:
Also, please check your forum messages, green icon, top right. 