yes absolutely. You can download the games and resume playing from the demo right away. I am not sure exactly which games you have purchased, but for Always Remember Me I'm 100% sure that you can resume playing without problems. For older games like Spirited Heart, once you have downloaded your full copy, is better if you restart a new one just to be sure.
As for different OS yes, you just need to email me and I can send you also the versions for Mac or Linux. For my latest games that use online activation you can download the demos for your OS and the code will work on any (you buy a license valid for all the 3 OS, no need to repurchase the game).
Hope I've answered to your questions