how do i find my iphone back up in itunes

The iPad and the 5s would only have backups on iCloud if you turned that option on. It is in Settings > [username] > iCloud > iCloud Backup. After that option is on, the devices will automatically backup to iCloud while charging if connected to wi-fi.

Regarding "yesterday I loaded the cloud on my PC" -- I assume you mean that you installed iCloud For Windows. Note that will not allow you to view contents of an iCloud backup. You can determine whether there is a backup by using the following instructions from Locate backups of your iPhone, iPad, and iPod touch - Apple Support

If you use iCloud Backup, you won't find a list of your backups on iCloud.com. Here's how to find your iCloud backups on your iOS device, Mac, or PC.

On your iPhone, iPad, or iPod touch:

• Using iOS 11, go to Settings > [your name] > iCloud > Manage Storage > Backup.
• Using iOS 10.3, go to Settings > [your name] > iCloud. Tap the graph that shows your iCloud usage, then tap Manage Storage.
• Using iOS 10.2 or earlier, go to Settings > iCloud > Storage > Manage Storage.

Tap a backup to see more details about it, choose which information to back up, or delete the backup.

You can choose which content to back up only from the Settings menu of the device that stores that content. For example, while you can view your iPad backup from your iPhone, you can choose which iPad content to back up only from the Settings menu of your iPad.

On your Mac:

1. Choose Apple () menu > System Preferences.
2. Click iCloud.
3. Click Manage.
4. Select Backups.

On your PC:

1. Open iCloud for Windows
2. Click Storage.
3. Select Backup.

The iPhone 5 cannot be updated beyond iOS 10.3.3 and I'm not sure that it is possible to restore a backup made with a newer iOS that you most likely had on the 5s.

First, it may not be possible for you to restore a backup from an iPhone 5s to an iPhone 5. If not, you will find that out when you attempt to do it. See: Restoring from an iTunes or iCloud backup when a later version of iOS is required - Apple Support That link talks about updating your older phone and in the case of the iPhone 5 that isn't possible. However, I wouldn't worry about it until you try to do the restore. If you do have a backup of the iPhone 5s (either of iCloud or iTunes) you will be able to use that to set up a newer phone when you get it, even if you can't use that backup to setup the older iPhone 5.

Follow the instructions in Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Since you don't know what backups if any you have, you might try to do the iCloud method first and then try the iTunes method and if neither is possible, you could restore using your iPad backup. You may first want to make a new backup of the iPad so you have the most current information. To backup the iPad, see: How to back up your iPhone, iPad, and iPod touch - Apple Support

Regarding

8. Is this assumption true: I am assuming that once I decide on what newer phone I am getting that there will be a way to get all the current up-to-date info from the dead 5s into new phone - that the two devices will “talk to each other - w/o using the iTunes version

That is not true. Nothing can "talk" to a dead phone. However if you have either an iTunes or iCloud backup of the 5s from before it died you will be able to use that to setup the new phone.

Find for what? To restore, see: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

otherwise, see: Locate backups of your iPhone, iPad, and iPod touch - Apple Support