I have an Acer E 15 (i7 5500U, 8GB and 1TB), but my windows 10 takes a long time to start and starts using 100% of my HD (1TB) for a short time (1 or 2 minutes). Must I buy another one or put an SSD for my Windows partition?
Yes having an SSD make everything feels faster, you can litrally see the loading time will be drastically faster because SSD's are much faster in loading the small chunk of data.
Of course you don't have to shut down the thing completely. Todays electronics, like your smartphone simply goes to sleep when idled. PC can do the same, wakes up in an instant.