Hello there!
First off before I say anything more remember the grader is only a guide, its not a garuntee that if you get an A you're suddenly in the number 1 spot so like most guides a little bit of your own judgment needs to be filled in too.
You if your alt image tags all have to have IPhone 6 case then that's fine you can probably ignore that particular point. Don't forget though you can always be more descriptive e.g rather that just having iPhone case you can describe it a bit more.
100 links does sound a bit much even for an e-commerce shop, but again you can use your own judgment, if you think you need links to every phone instead of categories go for it but if you can reduce them might be worth doing it or it can get confusing. Always try to put the user first if you think it would make the users like easier to have your site designed a specific way do that as Google likes the user and so should you!
There are some guide about the grader here on Moz if you need some extra help on them. If you are unsure of things you can always compare to competitors see what they are up to but remember just because they are number one doesn't mean they are right: what I mean is they might not necessarily have the correct design choice etc. but it can be handy if you are a bit unsure.
You might also find this blog post super helpful - http://moz.com/blog/open-site-explorers-new-link-building-opportunities-section
Another handy bit of software I recommend is Screaming Frog, its also free up to 500 URLs so give that a go!
Hope some of that helps & clears it up for you.