Synos will be no problem at all. To do what you are planning I would definitely have everyone young. Also be prepared with another tank for fish that don't fit in well. (Or have a good relationship with you LFS so you can trade for a different one.)
I found with the larger haps they tend to focus on the same fish... Usually for me smaller (IE half the size of the fish or smaller) OBs, or silver fish were always though as food.
Then just make sure everyone is getting food. It will be tough exspecialy for the synos... My larger haps will grab anything before it gets halfway towards the tank. (I used to have a syno in with haps, but he was never getting any food, moved him out and he did great.)
Anyways good luck, and for larger orders it might be smart to order online. (I like Erik Dyke for the larger fish, smaller I would go with say bluegrass, or atlantis. There are a ton of reviews out there. Check them out and find the place that has the most types that you want. If you really are going for 50 different types at once you likely will have to order from different places.)
And also remember small = more likely to work out in the end, but years of growing. Buying large = likley more problems but well you skip the wait. I tend to like to buy at least 3 inches or larger.
Finally check out your local clubs. See what fish they have that the market is flooded. (IE fryeri, T Reefs, German reds, Cap
borleyi all are 1 buck for 6.)
Finally
greenearthlawns, can you please stop shouting at us. (In other words can you please take off the caps.) Thanks.