I am looking at buying a Wagner Max HLVP sprayer. The jobs are staining a modest stretch of fencng and a larger staining project of an overhead pagoda-type structure. Is this a good choice or would you recomment something different?

I was a painting contractor for last 10 years of my work career.

If you are using HVLC cup gun, you will have to select correct tip,
You will need to thin the latex 50-50 with water, and keep paint strained to keep out all clogging.
If the tip is not reversible, then expect disassemble each time clog happens.
And you will be continually re-filling the cup.
And then if the surface is rough, the spray won't flow into the holes.
You have a mess coming your way.

Painting a fence: A roller is the only way to paint/stain rough surface.
Buy big hairy 1" roller cover from Sherwin Williams. Don't get the cheapo 1/4" thick roller cover because it doesn't hold any paint. The big roller holds a big volume of paint.

Now if fence is rough, like cedar, you need to thin the stain.
About 1.5 gallon water per 5 of stain ... and suddenly you have 6-1/2 gallons of stain which means you bought too many gallons of stain.
So don't overbuy the stain. And pick up 2 plastic bucket for mixing.
Empty gallon of stain into mixing bucket > put water into empty gallon > put lid on gallon and shake up > pour water into mixing bucket with stain > to mix: pour mixing bucket of stain back and forth between other mixing bucket until stain is mixed. Do this work on the grass where it won't run out onto concrete surface.

Put roller and frame on a wood pole that you took off the push broom. Now roll that stain onto every surface the roller can touch. Think of it like picking up quarters. If it was money, could you get the roller on that spot >> the answer is yes. Don't try to smooth it out and make pretty. Throw the stain on any way the roller can turn. Customers used to call that 'slapping it on' and I used to say, 'that's how it works, lady.'

Use a piece of masonite at the bottom. If you get stain on anything, wash it off immediately and use a wire brush on concrete surface or towel on smooth surface.

Wait for a day, because stain looks 100% better next day. And then go back with a brush and hit the spots you couldn't get with the roller. It will be faster and cheaper and fewer headaches than trying to spray latex stain with a HVLP cup gun.

To clean the roller: Leave it on the roller frame and wood stick. Turn on water hose and get the roller spinning until it's clean. Do this away from everything you don't want stain on.