SoundCloud explains this in detail here. Your play count represents the total number of times your track has been listened to by your fans, including downloads. Downloads are an internal stat only seen by you when logged into your Stats Overview page.
Yes! The Plays, Downloads, Comments, Likes & Reposts are yours to keep and SoundCloud rarely (if ever) removes them. If for any reason the number drops below the amount ordered within 60 days, we’ll fill you up for free in accordance with our 60 day free refill policy.
Not everyone can receive unlimited downloads on their Soundcloud Tracks. Free users can only receive 100 Downloads per track, while Pro users get 1k per month and Pro Unlimited get unlimited (obviously). To enable downloads, edit your track and under “Permissions” select “Enable Downloads”.