Want to stop a schedule download on iPhoto shared album

2.) If they are downloaded again, will be added at the end or by date taken? Hoping the former so it be easier to delete them all. Thank you

Shared albums will always be sorted by the date, the photos have been added.

I reached the limit (almost 1000 photos) and something popped up saying it would start again on some date.

There are different limits for shared albums - the total numbers of photos as well as hourly and daily upload limits. The limits are listed here: My Photo Stream and iCloud Photo Sharing limits - Apple Support

The upload should resume automatically once the time interval is up.