You can always migrate Moodle content somewhere else. There are various ways but the simplest is probably to use backup and restore. You can backup a complete course on one Moodle site and restore it to another one. So, yes, you can develop 'offline' on your Windows installation and then transfer to the Cloud install where you can have a few users (50 max). If you outgrow that then you can move to a bigger site. If you contact a Moodle Partner they can do this for you from Moodle Cloud or you can set up Moodle somewhere else.
The best thing is not to worry too much and just get started. Your data is safe. Make sure you have backups on your own machine if it matters to you though!!