Possible to have 2 iCloud accts on 1 Mac? / Possible to transfer iMessages from my old iPhone 5 to computer (already have a 6+)

I have two questions-

first, here is the background (kinda confusing so bare with me)

My devices:

• iPad air
• iPhone 5 (32 gig) (screen shattered but works fine, though I am not using)
• 6+ (64 gig) that I purchased / using since January

Our iMac is connected to my husband's iCloud account (it was his computer before we even started dating)

I rarely backed my devices to iCloud because

• many times when I tried, it always said I did not have enough storage available (and I didn't want to pay)
• I thought that you weren't supposed to plug in your devices to iTunes anymore for it to sync (I have an old, slow Windows laptop)
• I didn't think you could sync two iCloud accounts to one computer

Whenever I needed to update my iOS, I went in and manually chose to not sync many things to iCloud...to free up space.

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So now, here are my questions-

1. Is it possible to have two separate iCloud accounts on one iMac- if they are connected with two different users?

(i.e. Husband's user acct - my user account)

2. Is it possible to transfer text messages from my old iPhone 5 to EITHER computer - when I have been using a 6+ since January.

I did not transfer text messages to new phone when I got it.

I know this post is probably pretty confusing...but if you can tell- I am confused and cannot for the life of me get a good handle on how all this works. (very frustrating because I am generally pretty computer savvy)

I guess it's because I have always used Windows and I am new to Macs (which I love btw)

Any help or clarification would be GREATLY appreciated. I will purchase the additional iCloud storage if I have to but I'd rather not.

I know one thing that was annoying was that when I had my photos syncing to the cloud, they appeared on all my devices and took up a ton of space.

Please help!

Oh and I am trying to sell my 5 but there are some GOLDEN text/imessages on it. I know how to transfer photos/videos I mainly just want to transfer a few text messages.