Do interstitials hurt your SERPs?

Not just for 'breadcrumbs', but even on-page..

[McMasters]

So, if I run an image gallery, and on the first page of a subgallery, there are links to ten images, each of those images has its own page, breadcrumbing back to the subgallery, for SELP help.

Would I be shooting myself in the foot if I had half - or all - of those image page links use interstitials?

My main questions are these:

1> Does Google follow through interstitial links for SERP reasons?

2> Does Google downrank a page if it uses interstitials on its internal links?

3> How many links breadcrumbing back to a page is 'enough', so that further ones don't help? 5? 10? 20?

Thanks!