You may want to look into After Effects. It sounds like you’d get a lot of use out of the Puppet Tool: https://www.keyframer.com/index.php/2007/06/after-effects-cs3-puppet-tool/
Also, if you want Motion 3 you have to buy the whole Final Cut Studio. That isn’t a bad investment but make sure you know exactly what you are getting into.
Finally how old is your iMac? Motion 3 is very unkind to older video cards so be sure to compare your card to the minimum system requirements for Motion 3.
You can do the things you ask in both After Effects and Motion but for those specific needs you may find After Effects the best bet, although a bit harder to learn initially.
Be sure to Google comparisons between the programs as well to find other differences.