Access is very easy for Lonquimay - just park at the Corralco ski area car park. It is definitely not worth buying a lift pass for this one, as it is not a long day.
We stayed at Suizandina, which is very handy for Lonquimay. The couple who run it are Chilean-Swiss, and speak very good English, if that's a factor for you. We stayed in the dorms, which were en-suite 4 bed rooms! We paid to have the room to ourselves (effectively paying for a third person), but shouldn't have bothered, as we were the only people staying there (during the week it's quiet - weekends can be packed out though). We ate in the restaurant one of the nights, and the food was really good. There is free, but extremely slow, internet access in the main building. Definitely recommend the place. They also have a detailed map of Lonquimay available for purchase if you think you will need it.
You could use this place as a base for other volcanoes in the area, such as Sierra Nevada, or Volcan Llaima. However, to get to Llaima requires the "Ruta Interlagos" to not be blocked by snow. The day after Lonquimay we tried to get to Llaima and got the car stuck and the day was gone, as we had to turn around (once we'd dug it out), and it's a long trek round by any other way.
As with access, the route is very straightforward. We followed the easiest angled chairlift I have ever seen, then followed a curving gully to avoid the steep section up the next tow. From marker at the top of the lift, we cut diagonally up and right across the large east facing triangular face. The upper secion of the face became steeper, and we ascended the last section carrying the skis on a very shallow rocky ridge. This took us to the rim of the very large crater, where we turned south for the 5 minute walk to the summit at 2865m.
This was the only hill where we used our ski crampons, and it is just as well we had them. The lower easy angled slopes were quite icy. With the ski crampons - fine, but otherwise we would have been carrying the skis from approximately the top of the lifts. By the time we got to the top, the sun had softened the snow a little, but the easier angled section above the ski area was still quite firm. The steeper slopes were fine.
With skis on right at the summit, we cut back a bit towards our ascent route, before skiing the superb face. Our descent route avoided the steepest section directly below the summit, but in reality, you could ski anywhere on it, if snow conditions allowed.