Migrating from my old iMac to new 21.5" Retina 4K

I have just replaced my 7 year old 21.5" iMac running Sierra with the new 21.5" Retina 4K iMac. I migrated my old mac to the new one using an ethernet cable between the two, which worked fine. The reason I upgraded was simply because my old one was running extremely slowly, taking up to around 40 mins to boot up. Also when I downloaded App for WhatsApp to my old machine the icon for the app appeared covering the Applications icon in the Dock, so my Applications folder looked like App for WhatsApp. Now that the new Mac is set up, the same thing applies. I cant see the Applications icon, although when I click on it the Applications folder does oped normally. I am wondering if, when I migrated my old iMac, it brought with it any problems I may have been experiencing before. My other concern is speed. Before any problems, my old Mac would boot up very quickly, but now it takes 1m 12 secs and I have to watch a white progress bar. This may not seem a long time, but I would have expected it to be quicker. Also opening programmes takes longer than I had hoped. Mail - 37 secs, Photos - 72 secs, Word - 35 secs etc. Am I being unreasonable. I love the iMac and just want reassurance that all is well. One last thing; can anyone tell me how to delete the App for WhatsApp icon covering the Applications app in the dock.