Camera Raw is a plug-in that Photoshop requires in order to open and allow you to make adjustments to raw images. Lightroom does not use the Camera Raw plug-in because that technology is part of the Lightroom program. It is possible to do all of your work using Lightroom, and it isn't absolutely necessary that you have Photoshop. But there are some things that Lightroom cannot do that are easily done in Photoshop. And there are other things that Lightroom does but Photoshop performs those tasks much more easily. The two programs work well together. You can start with Lightroom and decide if it meets all of your needs. If you don't want go with Photoshop as an external editor from Lightroom you could consider Photoshop Elements. It offers many of the features that photographers need and it too is a good companion for Lightroom. I use Photoshop and Lightroom, and do most of my work in Lightroom. But it's nice to have Photoshop available for the things that are needed. For example, Lightroom cannot create panorama images. Photoshop can. It is sometimes easier to remove blemishes or objects using Photoshop. It's just something that you will have to decide for yourself. You can download a 30 day trial version of Lightroom and evaluate it. Then it will be easier for you to decide.
As Jim said, Lightroom has Camera Raw already built in to it. And Lightroom contains profiles for your cameras, six for the 70D and five for the Stylus One.
Being unfamiliar with Adobe products, my question could seem curious!
Yet you replied with a very high accuracy.
Now I understand better the positioning of these three products.
I will adopt the approach you recommend.