A yeast starter is best made from the juice the yeast will be
living in. If that juice is not available try apple-juice.
The yeast needs all the things that is used for a healthy fermentation like nutrient, sugar and acid. But the best thing is not to use sulphite in the starter.
A starter will then start fermenting the juice just like in the real must only in a small quantity. Air is introduced by making the starter in a open bottle.
Each 20 minutes or so the yeast will multiply so after one to two days you will have a healthy colony which is then added to the rest of the must.
I wrote an article on the how and why of a starter on my web-log.
Look in the archive (right side on the page and on the archive page look at the augustus 24 entry:
http://wijnmaker.web-log.nl/wijn_weblog/2007/08/24/index.html)
There you will find pictures also from several healthy yeast starters, so you will know how it should look.
Yeast should not be floating around in clumps but the yeast should be 'dissolved' in the yeast.
Maybe your yeast was not working at all. And just a low part of the yeast was still alive so therefore the fermentation is starting very slow.
You could at this moment de-hydrate some more yeast and add it to the must to help speeding things up. There is no problem in adding more yeast.
I wonder if your must is protected by sulphite.
If not: do so now. It could be that your yeast starter was not working and that a fermentation has started with wild yeast that was in the must.
You could also wait and see how it turns out.
But if this is a large batch I would not be willing to take the risk.
I would add more yeast.
Luc