Editing photos before uploading to wordpress

Hi Mac Users

Can anybody tell me how photos have to be edited correctly before uploading them to a www.ads-software.com blog? I am using the following setting:

Theme: Twenty fifteen
Computer: iMac (newest generation)
Other devices: iPhone 6, iPad 2
Digital Camera: Fujifilm X100T and X-T1
Photo Editing Software: Lightroom and Photoshop CC

My problems are the following:

– Photos shot with my digital camera in portrait orientation are displayed in landscape orientation on my iMac. The images are displayed correctly on my iPhone and iPad. When I edit my photos inside wordpress, I can turn the photo to portrait orientation, but then they are displayed in landscape orientation on my iPhone and iPad. I have found some posts in the support forum that suggest to edit the picture first before uploading. I would like to now, how you edit photos before you upload them and which software you should use.

– Uploaded photos have a poorer quality than the originals. I have read in some posts in the support forum, that this is because wordpress scales the images down to the max image width of the theme in use (column width). It is better to resize the image first, before uploading it. Which dimensions would you recommend for pictures and the theme twenty fifteen?

– I have read that the image resolution should be not more than 72ppi in order to not waste storage space…is it recommendable to set the resolution to 72ppi for pictures that are going to be uploaded on wordpress?

Thanks for your advice.
Andrea