If you've got jump pack models, I'd definitely use the jump packs. You need the mobility to keep up with the crisis suits that are going to hop all over the place, and it reduces the number of shots that dug in Fire Warrior squads will have since you'll be able to get stuck in a lot faster. If you have a Chaplain to lead the assault squad, there's actually a pretty dirty trick you can use. Give the squad meltabombs. When you charge, you still need 6's to hit the skimmers, but you get to re-roll the misses. Enjoy the fireworks.
As for scouts... five men CAN be effective, depending on their armament. They make for a passable anti-infantry heavy weapons team when you've got four with bolters and one heavy bolter, although I've found there are generally better uses of the points.
If you've got points for a drop pod and a dreadnought, I'd consider taking one. Assault cannons are statistically more likely to crack armor than a lascannon now, and if you make it a Venerable dreadnought and give it tank hunters, you'll have a very menacing all-rounder. The drop pod not only will give it a tiny bit of cover from stuff opposite the drop pod when it comes in, but it'll let you put the dreadnought more or less where you need it. The Tau don't have any anti-armor close combat weapons such as power fists or meltabombs, so a dreadnought will be totally uncontested in close combat against them. The biggest threat comes from Krootox in close combat, and it's pretty negligable even then, since they need a 6 to glance the vehicle.
Oddly enough, Land Speeders work quite well against devilfish. While Space Marines may be one of the more forgiving armies to play in general, they still do require some tactics, and the use of fragile vehicles such as Land Speeders definitely falls into that catagory. If you have a speeder with a multi-melta and make effective use of what cover is available, you'll find your 65 points quite well spent when the melta connects with a loaded devilfish or a hammerhead. There tend to be bigger threats on the table to the Tau player, such as your infantry, so the odds of them actually focusing meaningful firepower on the skimmer is low enough that it should get there so long as you're careful about it.