With all the problems others are having with random attacks, I created a character to embrace it. He's decked out in Heavy Dawnguard Armor with dual enchantments. He's armed with dual enchanted Dwarven Crossbow, dual enchanted DG war axe, and DG shield. Ingjard is his follower and she's decked out in dual enchanted heavy armor and carrying dual enchanted crossbow and dual enchanted DG warhammer. The pair is somewhat on the OP side, but hey, we're trying to keep NPC's from dying here!

I like to find out from others at what stage in the DG quest line are the attacks the most frequent and deadliest?

Right now I haven't started Chasing Echoes yet. I am seeing random attackes in daylight in the wild, Mysterious Traveler in towns late at night (love that guy!), and some attacks at major cities' gates, especially in the middle of the night. I have to do tons of fast traveling or travel by carriage to trigger these attacks. Do they become more common further in the questline? Does it take a few days between each attack?

My favorite vampire quote so far: "I love it when your food just falls into your arms!".

i honestly don't think that the attacks become more or less frequent during the storyline, but just become more or less frequent at random times.

Walking around during the vanilla MQ dragons could be everywhere, or nowhere at all. I think it'd be the same.

But my personal situation, I had more attacks at the beginning of dawnguard in the wild.

You're probably at a good spot right there. I am past Chasing Echoes (up to the Darkfall Cave part), and I hadn't noticed an uptick compared to before CE. Besides, in the next step you'd be forced to ditch Ingjard for a bit and traipse around with a vampire chick. For RP purposes that might not be ideal for your character.

Start shooting the sun with bloodcursed arrows. That'll do it.

I had to wait until level 35 before I had one...and I may have lost Sven to the vamps, although he could have been drunk and fallen down the tavern stairs in Riverwood. If no one cleans him up soon he's going to get dumped in the river.

Thanks for the replies. I've been experimenting. So far, it looked like every 3 days for the vampires. I was lucky enough to get the Mysterious Traveler and vampires in Rorikstead in one night. I have encountered the mysterious traveler at less than 3 days interval. He's fairly easy to trigger. Fast travel or use the carriage and go to a town after midnight. If he's not there, go into a building and exit. Most of the time he'll show up. My favorite encounter so far was in Falkreath. I walked out of Deadman's Drink into the middle of the street and waited for him. It felt like a gunfight scene right out of a Western flick.

One of the most reliable 'hot spot' for vampires attack is Riften Stables. Typically I get a couple Frostbite Spiders or bears thrown in with 3 vampires. The hardest part is keeping Hofgrir Horse-Crusher from getting killed. I found that it helps to run east into the woods to meet up with the vamps and take at least 2 down before Hofgrir arrives.

I think this is a good place to stall the quest, too. It does fit better from a RP perspective.