This can be involved so bare with me.
Tourweaver does not compress your "main" panorama image. So you need to make the decision before importing into Tourweaver.
If you are going to display fullscreen (in my opinion) you need a minimum of 4000x2000 pixel image in dimensions.
Compression of this image is relevant to and a restriction of the colour within the image. Some images will compress much harder (to end up smaller in file size) than others of the same pixel dimensions before showing obvious compression artifacts.
Now "if" you choose the Tourweaver publish option to show a reduced sized version of your "main" panorama image you can select say 50% of the original (2000x1000) because your smaller display (before going fullscreen where the "main" panorama image will be shown) say at a viewer window size of 640x480 or whatever you choose. You get the chance then to compress the "50%" version of the image (within Tourweaver) with the .jpg preview window and adjust the slider to suit your requirements but this ONLY affects the 50% version NOT the original imported panoramic image that will be used for fullscreen viewing.
This then will give you two folders within your PUBLISHED "source" folder named 1 and 2. Folder 1 contains the 50% compressed version for small/normal window display and the folder 2 has your panorama image you imported into Tourweaver uncompressed (although it gets renamed slightly) it will be the exact file size (weight) as imported.
OK, if you can get your head around my explanation then you should be heading in the right direction.
How do you compress and resize an image to meet a target goal?
I personally recommend a program called KissMyImage www.kissmyimage.com
because it is the only program that lets you set the maximum files size target required. It also resizes and does it in a correct mathematical way.
What is a good size for a panorama image per scene?
That is a hard one because you must allow for download speed vs customers exceptions vs viewing quality. I believe for a "tour" you should be aiming at under 2mb per 4000x2000 image with 1 - 1.5mb optimal. For single (non tour) panoramas I think 3mb is a fair target at 6000x3000 pixel dimension.
Remember "if" you have gone with the smaller 50% viewer for your small/normal webpage view the end user doesn't download the fullscreen larger files unless they choose to view the scene/s fullscreen. Meaning no bandwidth wastage and faster downloads etc.
The style of image (cubes or spherical) imported makes no difference to the file size.
It is possible to re-compress a panorama image "after" publishing. This is the image in the 2 folder. You can open in Photoshop or KissMyImage (compress) and replace it back into the folder just be sure to keep the (exact) same file name. It is NOT
possible to resize this image after publishing because it will destroy the hotspot positions.
Must not be saved as a progressive .jpg only baseline.
I hope this makes sense and gets you on the right track.