platon, I can help you with 1,2, and 5.
1) Always use an aquatic rated surfactant. With diquat being a little over $100 a gallon, and the aditional cost of the copper product, surfactant's a cheap addition that can only help.
2) Just my personal experience, but submerged application is definitely the way to go when treating anything subsurface. I do surface spray from a utv when the water's too shallow to get a boat to.
The chemicals applied, will slowly float down if surface sprayed, but in dense areas, it doesn't always get to the bottom and eliminate it. Wind also affects surface spraying, by causing the chemicals to drift, and that can make proper coverage hard to gauge. Wind also affects the actual spraying, and the amount of chemical mist that may blow back at you. Gear up for surface spraying.
Below is what I built to handle subsurface spraying. A boom rig can be anything that'll spread 2-3 drop lines out for a more even application. You could probably use a 25 gallon spray rig in 12' jon boat. I sprayed here for years in one, it just took longer. If you go that route, I would highly recommend getting at least a Northern Tool 5.5 GPM NorthStar pump with a 2 year warranty. Copper and diquat seems to eat 12volt pumps alive, and require a great deal of cleaning between usages. I love the pumps, but asking 2 years out of them is a lot.
I now use a siphon system because it allows me to meter flow, and keep potential caustic chemicals away from anything but the 3 discharge hoses. To clean the hoses only requires a siphon shutoff.
I like my hose's discharge 2-3' under the surface. I use heavy duty chem hoses, so they don't need to be weighted. If you go with a lighter hose, it will need to be weighted. The only issue with this, is to make sure your hose ends are above the bottom. If they drag bottom, you'll be stiring up silt and reducing effectiveness.
5) Our big pond is 11 acres, and I've stocked 110 grass carp over the last 5-6 years. They never controlled it. Coontail's not a preferred meal for them. If you get some, don't overstock. The permit will always allow you to get more, but it's hard to get them out if you get to many.
Tilapia may be a tough find right now, but they could be put in at any time. It's getting late in the season, and forage size might be all that's available. If you get them, I might pick fewer and larger if available. If you've got a heavy LMB population, forage sized tilapia could be Scooby snacks in less than a week. Also, the high water temps make transporting and stocking fish problematic.
Just a DIYer, so others feel free to correct anything I was off target with.
