I am making my first 3 tier, 8in, 6in, 4in. I have the cardboard dowels and cakeboards, will this be sufficient for this cake??
Your input would be greatly appreciated.... 
I suggest you watch this superb video by Sweetwise, Inc.
http://www.youtube.com/watch?v=KdzLN5hjulo&list=PL178BA8A7498017F9&index=5&feature=plpp_video
Once you have watched the video, you should have a very good idea of whether or not your preparations have been sufficient.
Assuming you're doing a straight stack?
I use a ruler to check my distance between tiers since being a little off can mean a leaning cake. I measure off my dowels by inserting one, marking it off and then removing so I can cut the rest to match. I dinged a cake once cutting a dowel in place and had to patch it so lesson learned!
Apti's video link is a great one =)
You'll do fine! The first one is the scary one
Quote by @%username% on %date%
%body%