Do I need to manually back up my iphone photos if I have auto downloads already set up in iphoto?

If you have the iPhoto Photo Stream preference pane setup as shown in this screenshot all of your photos taken on your iPhone will be automatically imported into your iPhoto Library:

Therefore you don't have to manually import the photos. However, if you take any videos you will need to manually import them into your iPhoto Library as Photo Stream does not include videos.

#4 - if you take 1500 photos in one month all will be imported to your library. However, only the last 1000 will be retained in the Photo Stream.

Can't help you with #7 as I don't use either. But I don't think so.

This Apple document should answer some of your questions: iCloud: Photo Stream limits

OT

Good questions!

SInce you are having Photo Stream, you may want to backup your iPhone to iCLoud. to be on the safe side, see: iCloud: Backup and restore overview

1) If I take a picture with my iPhone it goes to both my camera roll and my photostream (yes, photostream is on)... is this correct?

Yes, photos you take with the iPhone will be stored in the camera roll, and the camera roll will be automatically added to iCLoud and synced to your devices.

2) My photostream is limited to 1000 photos. These photos exist on the cloud aren't necessarily saved to my computer... is this correct?

My photo stream is limited to max 1000 photos and only the last month of photos.

If you enable automatic import on your mac, these photos will be stored on your mac automatically in monthly events in iPhoto. Or you can import manually, what you are seeing in the My Photo Stream album.

See: iCloud: Photo Stream FAQ

3) I have automatic downloading set up via iPhoto on my MacBook Pro. When I do this ALL photos I take are downloaded by my computer as long as I've connected it to the internet at some point recently... is this corret? If they are downloaded, are they downloaded from my photostream, or are they downloaded as they come in?

All photos currently in iCloud will be visible in the Photo Stream, when it is enabled on your mac, and with automatic import they will be added to the monthly events, as soon as the mac syncs with iCloud.

4) If I go over 1000 photos in a month in my photostream, does it save ALL of them to iPhoto or just the 1000 most current?

When you reach 1000 photos in My Photo Stream, the oldest photos will automatically deleted, so you should sync your phone before that happens.

iCloud: Photo Stream limits

In other words, in iPhoto I see a section labeled, for example, "May 2013 Photostream". If I took 1500 photos during that May timeframe, would they ALL be there or would only the 1000 that constituted my photostream at the time of download be in there?

You can sync more than a 1000 photos per month, only make sure, you sync often.

5) If a photo is show in iPhoto it is permenantly downloaded to my computer's harddrive... is this correct?

It is downloaded permanently, as soon as you are seeing it in an event in iPhoto, not if it is only showing in the "My Photo Stream" album.

6) This is the biggest one. If I have auto downloads set up between my iPhone and iPhoto, is there any reason to download photos manually? Everytime I download photos manually it says I have a bunch of duplicates. They all seem to be duplicated in my photo stream, BUT others are not duplicated and seem to download at the time of the manual operation, which makes me think that they autodownloads aren't downloading everything.

One good reason to download manually would be the download speed. It is just quicker, and you are not risking transmission errors. Also, you may have more photos in your camera roll than in the photo stream, because you could have deleted photos from the photo stream. The duplicates should be no problem, if you exclude them from importing.

7) Do photos I edit in Snapseed or Instagram get downloaded automatically or do I have to put them somewhere for that to happen?

I do not use these apps, so I cannot be sure, but usually you will have to save edited photos back to the camera roll, to be able to sync them, either with Photo Stream or by manual sync.

Regards

Léonie

So just to clarify, if I have automatic downloads set up, will it only download photos in my photo stream or does it download photos from elsewhere?

Automatic downloads (from Photo Stream) will only downlosd the Photo Stream photos.

What I'm worried about is that my phone is saying over capacity on iCloud.

Are you storing other documents in iCloud? Check your iCloud settings in System Preferences.

I do semi-regular downloads with my phone, but I'm worried that I'm taking too many photos and that I'm missing some. It seems from Old Toad's response however that every picture I take should get saved to my iPhoto automatically

Your Photo Stream will show the last 1000 photos you have taken, each photo for max. a month, and within this interval your mac should be online to download them, when they appear in the stream. It is unlikely, that you will miss any photos, if you do not take your mac offline for weeks, or shoot more than 1000 photos within a very short time.