Helmet *has* to be comfortable. I bought a Shoei Hornet because it was the only dual sport that fit and wasn't going to be torture after a couple of hours. Wear it as long as you can in the shop because 30 seconds just isn't enough to really figure out pressure points. It has to be snug to work, so don't be shy about twisting it and feeling your cheeks, crown of your head and stuff moving around. If the helmet shifts around that's probably too loose. So since it has to be tight comfort is going to be the key.
To my dismay the one that I got wasn't the cheapest option, but then again you only get one brain so $200 or $400 is kind of, well, a no-brainer. I used the same logic when buying a welding helmet, I'll forget the difference in price if I get cataracts from the $100 one. Any helmet you buy will (or should) have DOT and Snell ratings, so they should all protect in theory. So don't necessarily be afraid of a low cost one if it fits well and has features you like. I almost always buy Bell bicycle helmets because they fit my melon but the Bell motorcycle helmets feel like my head is in a vise.
One thing that is really nice on a helmet is having a stop on the shield that positively holds it with just a small gap. The vents are never enough to really keep it cool or fog-free. I find that on cold mornings having the face shield cracked a little above the chin guard works like the defroster on your dashboard. I actually prefer for dual sport if you're only doing small lengths of pavement and not a lot of highway to run a dirt bike helmet and goggles instead. I don't really like having the face shield down and I don't trust sunglasses on the highway, so the clear shield is useful for that.
I never bought real moto boots and just wore my steel toe Redwings. Having shin protection would be nice on trails and having skid plates would be good for pavement if you dump it and providing additional lower leg support. Getting your leg under the bike is a real problem and work boots don't help with that. Is this critical? Yes and no. My decision was to spend more on the helmet and fill in jacket, pants and boots until I could afford them. If I dump it on pavement the boots being leather above the ankle will a little help and my pants come down over. But real MX boots would be better since your ankles are nowhere near strong enough to hold up a big dual sport, although they are less comfortable on pavement. There's really no one perfect setup, you figure out what works for you.
I ended up with an Alpinestars jacket and Klim pants. I put all the armor in both, hard plates where they were available. I figure the critical ones are the back, followed by elbow and hip. The back plate is to keep your from bending backwards and breaking your spine and of course impact protection. The hip and elbow are for sliding on pavement. I have shin and chest armor, too. The reason for the chest plates is to prevent a handlebar or tree branch from spearing you. I went with the shin because I haven't got high boots. A flak jacket under a riding jacket is another way to go.
Don't forget about gloves, too.
You can see what this stuff looks like here (I happen to be selling my bike and gear FWIW):
http://www.risingsun4x4club.org/forum2/showthread.php?t=25300
