There are two ways to get the two newest coasters done.
One, you can head straight to Verbolten to try an avoid any lines and then head to France to ride the Griffon. The issue here is the line length for Verbolten is variable and the line moves fast and it has a somewhat engaging queue. Griffon on the other hand has a much slower moving line and it's boring and it gets longer as the day wears on.
Two, head to France and hop on Griffon first, then go ride Verbolten. This is actually the better plan more often than not, but it means you are chancing a long line at Verbolten. However the speed and themeing of it's queue help offset that issue.
Typically you won't have to wait in exceedingly long lines at Loch Ness, Alpengeist and Apollo's Chariot. But Howloscream has a way of through those trends off so you could see some long lines.
Apollo's Chariot is a MUST DO at night. Also, sit in the back two rows on the right side of the train for the most airtime.
Sit in the front row on Verbolten and Alpengeist for some great visual fun. If you get a chance to do them again, ride both of these in the back for more speed.
Ride Loch Ness towards the back of the train for a much much much smoother ride. Also, if you have someone tall in your party, sit in the front seat of the car you choose on Loch Ness. Even for someone of average height the back seats of the cars on Lock Ness are a little snug as leg room goes.
For water rides, don't miss Escape from Pompeii, if it's open. There is a haunt in the bottom of the show building and there have been years when they have kept the ride closed all day during Howloscream.
Also, make sure to ride the Log Flume. It is a classic and one of the best one's I have every ridden. The drop at the end is fantastic.
Roman Rapids is not a great raft ride. It's short and uninspired. But if you like those types of rides is will suffice.
All of the water rides close early during Howloscream so get them done before 5:00.
Unfortunately, I think the This is Oktoberfest show has ended for the season, but if it is running it is a park tradition and not to be missed. It shows in Das Festhaus.
When the Haunts open, head for "13, your numbers up" first as it is filly indoors and the remaining daylight won't hurt the experience. Plus, this tends to have the longest lines.
Along the same lines, Bitten and Catacombs all work during the daylight as well.
Don't even think about going through Deadline, Root of All Evil, and Cut Throat Cove during the daylight, unless you want to do them twice. But even then, you will end up with two less intense experiences, one from better vision and one from knowing whats coming, versus one intense experience.
The shows for Howloscream are mixed. The show in Italy, Dig It Up, is in a word...strange. It wasn't to my liking. But the show in Das Festhaus is pretty fun and entertaining so long as you like tongue and cheek humor and cheesy themeing.
Finally, what I would call the flagship show, (it has been around since the first howloscream event in one park or another) is Fiends. Fiends is a much more adult show with naughty nurses and a great deal of sexual innuendo. But, if you are an adult and like edgy humor and a high paced show, this is the only must see show for Howloscream.
The only other things I will note for you are food options:
Festhuas and Smoker's Traphouse are the best meals so long as you like German food or Barbecue.
Italy has some pretty weak food. Lots of overcooked pasta and heat lamp chicken parm.
Another unique dining option is Grogan's Grill. If the weather is cool enough, the beef stew served here and the pork loin with carmelized onions are good cool weather options.
Hope this helps and I hope you have a great trip!