There are a bunch of roles at an orthodox wedding that are filled by whoever you choose to fill them. Most of those roles will be halachik witnesses, and must therefore fit certain standards of being a kosher witness.
You may have a lot of pressure to honor great (or not so great) Rabbis, Presidents and dignitaries who are attending you wedding, and I'm the last person who's going to tell you to get on the bad side of the Prime Minister of Malaysia. BUT, I found it to be more meaningful to have close friends and family fill all of those roles.
As far as who will serve as witness to the kiddushin, the tanai'I'm or the yichud, just make sure to find people that are kosher and reliable. Close friends ( and even Rabbis) can fill this role well. For more information on witnesses, checkout this chabad page.)
For the sheva brachot, this is when I think it is most meaningful for family members to get involved. The standards are much lower - and even your athiest grandfather can say one if he can handle the hebrew.
Make sure whoever you are giving a kibbud to knows about it. He should feel comfortable with the role, and see it coming. Do not surprise your high school Rebbe with the honor of being your mesader kiddushin! Tell him in advance.
I found it helpful to have an extra witness in mind just in case on flaked out, and in fact we had to resort to one of our bench warmers at our wedding which averted a possible disaster. Make sure your best friend or shamash has a list of kibbudim and will make sure things run smoothly.
Aside from that, sit back, relax, and enjoy the partay!