Yes you can place cubes directly into the flood tray. You can start with small cubes and work your way up to bigger ones. Make sure you peal the plastic off before inserting a smaller cube into a bigger one. In this case I think a passive drip system would be better than flooding the tray. You would use the same system except instead of pumping water into the tray you would pump it into a manifold and put a drip line to each cube. Then you would use a passive drain in your tray so all excess would flow back into your reservoir. They also sell
THESE that could hold more roots. If you want to use a system like this all the way through I wouldn't veg for very long due to running out of space for roots. Another option would be to veg like this and then Fill 2 gallon pots with some coco, throw those on your tray and put your large cubes with drippers into the pots. You could have some pretty nice plants like this.
I've heard good and bad about sure to grow. It dries out well so your roots get a lot of oxygen and it is ph nuetral. On the downside it costs a lot and cant be reused plus I've heard of algae problems with it. Personally I prefer hydroton which is the best medium IMO because it would really get a lot of oxygen to your roots in between floods or with a dripper system. You need a lot of space for roots with hydroton because they blow up which is good. You could build an awesome 9 bucket ebb and flow system on a 3 x 3 table. Just connect all the buckets together and put a 27 gallon tote under the table with a pump in it. Fill the buckets with hydroton this way your roots would get a chance to get totally oxygenated between fills.
I use DWC tho it kicks ass you can get same or better results if you use a good air pump.
IF