Huge problem with contacts and iMessage on Mac Os Sierra

Hi.
I had recently purchased a 2013 MacBook Air because I wanted to start using Mac OS and because I needed a mobile laptop solution when I am on travels and under way so I don't need to carrie my huge gaming laptop around, so, I thought the light waight MacBook Air would be a good solution and it really is up to this point.
Sadly, there is something bugging me and I can't seam to find out what the problem is. Beware that this might be a longer post.
I have a problem importing certain contacts into my contacts app on the Mac via iCloud.
For better information, on the iPhone I have 4 mail accounts,my iCloud account, my hotmail account which is my primary E-Mail ACC and microsoft account for windows, xBox and so on, and two other Mail addresses which I need for newsletters, spam catchers and so on, it's another outlook and google mail address, please note that the primary account doesnt have the @outlook.com, but the @hotmail.com address.
All of those account have contacts linked to them, but the most important ones are at the iCloud and hotmail addresses.
So, now to the problem. I started setting up my iCloud with logging in and importing things like notes, reminders, mail, calenders, iCloud Drive and so on.
I than started my Mail app and entered my hotmail account so I had the @me.com and the @hotmail.com addresses set up. I than tried sending an iMessage to a friend, for better recognisation. let's call him Mike Smith.
So, I wrote the message but i got an error saying that the message couldn't be send. Than he send me a message which arived. Strange thing was, that in the conversation list, I had Mike Smith and another number which was his infact but it was showing like a completely different conversation, while on the iPhone, the message came in as Mike smith. I than tried typing a message to the other number, and it worked out fine, I was heavily confused at that time how a number can be wrong, but at the same time be right.
Problems started getting bigger after that, I noticed that not all my contacts had synced. Normaly I should have around 160 contacts, but just 82 were in the contacts app, and they also had that phone number thing with the iMessage going on.
I than went to the system control panel under internet accounts, chose my hotmail account to sync the contacts, but I just could sync notes and mail, which worked fine as far as I could see.
So, my questions are
1. How can this iMessage thing be and what can I do to solve it.
2. How can I easily import my Hotmail contacts without making a huge mess in my iCloud?
3. Is there a way to transfer all contacts over to one account so I don't have that problem in the future?
Already thanks in advance, I hope that someone can help me.
Greetings Moritz.