That's cool. Will be a great layout regardless. I'm looking to get slate for my 100. The plants are doing great for being less that 1wpg, lol.
If you have a petco near you, they should have a pack of "various aquatic bulbs" the onion plant bulb looks like, well.. an onion. all the other bulbs will just grow mold and never sprout . They were 3.99 a pack but if you pick out the right one you should get 2-3 onion plant bulbs. Mine have grown from a bulb to a 3" plant in like 2 weeks.