If I get a new MBP, can I install aperture. So I can see and move images

You can open the library in Photos; if you previously got Aperture from or associated it with the Mac App Store, you can also download it to the new Mac and use it to access the photos.

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,...will I be able to install aperture, and use it to read the ext HDDs so i can access my images, and migrate/move/change them to referenced images. Or am I screwed with tens of thousands of images trapped on the HDD

Which version of Aperture do you have on that old Mac?

Only Aperture 3 has been sold from the AppStore. Check your Purchases History, the fourth tab at the App Store, if you are seeing Aperture there. If Aperture is not in your Purchases history, you will not be able to install Aperture 3.6 by downloading it from the AppStore, and only Aperture 3.6 will run on a new Mac.

But as Niel said, the new Photos for Mac application will be able to open your Aperture libraries. This document shows how your libraries will be migrated to Photos for Mac, see: How Photos handles content and metadata from iPhoto and Aperture - Apple Support

All your edits will be in place, your albums, most of your metadata tags.

If I buy an up to date apple,...will I be able to install aperture, and use it to read the ext HDDs so i can access my images, and migrate/move/change them to referenced images.

Aperture 3.6 is still running well on MacOS X 10.11.4, there are a few glitches like upside down thumbnails in list view, but referenced images are still working well, as for as I can tell. You can still turn managed images into referenced images and consolidate referenced images as managed images.

And if you open a referenced Aperture Library in Photos for Mac, the referenced images are working as well.