I had done Kili some years ago but this was my first proper mountain and I am happy to admit that I had a fair few sleepless nights in the run up to departure. I was still very concerned how I would cope with technical / climbing elements of it. Although I have spent quite bit of time in tough and / or cold places, until you have done an expedition you can never really be sure how you will cope in that type of an environment. I have also always been a bit casual about looking after myself and whilst you can get away with that if you are strong and fit in less demanding conditions, I was concerned as to whether my personal admin would be up to the task. I had been doing quite a lot of fitness and strength training recently so I was fairly comfortable on that front although not sure what sort of shape other people who did these mountains would be in. As it turned out, I had little to worry about!
Aconcagua is high (the highest mountain outside the Greater Himalaya) but not that technical. There are a few places when getting to the summit when there is some light scrambling but otherwise it is just a trek although you will need to be comfortable in crampons as there is snow and ice on summit day. Summit day itself is pretty tough in that altitude really does start to impact once you get above 6k but there is nothing to be afraid of.
It is exposed to strong sun (as it is fairly near the equator) and a lot of wind which minimises how much snow or ice remains on the mountain. As such the lower slope and surrounding peaks are all scree and rock meaning that it is not a classically beautiful place. But the views do become dramatic once you get up high.
Mendoza is a great area for things to do after the climb and you are not from the Lake District which is a wonderful area – see my Post Aconcagua page.
Decisions here are route and style of trip. The best route seems to be the traverse where you go up the Vaccas Valley route and so avoid the crowds and then out the normal route which is significantly quicker and it is always good to do not return the way you went in.
Because the mountain is not too large there is quite a large range of options in terms of how much support you want. Pretty much everyone uses mules to carry quite a bit of gear up to base camp but above there you can chose whether to be self-sufficient or get local guides and porters to do the carrying and cooking. If this is as high as you are going to go on a mountain, these more heavily supported expeditions are great as you preserve your physical and mental energy. If you are going to be doing other, tougher mountains you really should be looking to do this with minimal support as you learn much more that way and so gain much more experience in preparing for challenges ahead.
The Vaccas valley route starts with a few days trekking up a gentle gradient before turning left into a side valley. There is a steep path up to a col and then a gentler final run into base camp. It is carry and cache from base camp to acclimatise and provision the upper mountain before checking the weather to fix a summit day and then a push for the top.