Now enjoy and sorry for late reply.
For 1) I don't think there is a need of change in index.html page because it simply redirects to your website registration page.There is no such hard coding inside index.html.
For 2) If you are talking about icon url used inside index.html then you can change according to your preferences. And if you're talking about app icon on phone screen used inside manifest file then I don't think there is need of any changes but you can add 56x56 84x84 & 112x112 size icons inside zip file if phone not showing icons properly.
For 3) Yes KaiAds is necessary if you want Kaiostech people team to test your app immediately and to give review of your app immediately.
I know You will didn't like the kaiads but kaios team will like it and fullscreen is most easiest way of showing ad without any heavy editing on JavaScript.So if you use kaiads you have to sign up for kaiads ssp then you will get a publisher I.D which you have to copy & paste on kaisdk.js file that's it you have successfully setup a kaiads on your app.If you don't like fullscreen ad you can edit according to your preference chevk out this website-: https://www.kaiads.com/publishers/sdk.html
For 4) Don't be so scare about report.txt you just to have to write about working and features of your app inside txt file then optionally write about issues or error if you are facing while running of app that's it.
Sorry to say but these are all tantrums of KaiOS app submission just for publishing because they are not big as android so they have to do these tantrums for their sucking profit.
I understand you want to manipulate directly from your website and your related server without making separate app even I tried this method for my website but most of times this app submission website rejects even after enabling all tricks I don't know why.
If all the above paragraph said by me isn't true and you were trying to upload via *New Packaged Option* then maybe browser is not compatible with app submission website. I mostly do app submission upload from *New package option* via Firefox browser.
But Kaiads is only supported on only Kai device as per my experience I never tried on website because I rarely get to choose hosted app uploading so I don't know sorry.
1.https://developer.kaiostech.com/getting-started/build-your-first-hosted-app/pwa-to-hosted-app
2.https://developer.kaiostech.com/getting-started/build-your-first-hosted-app
3.https://developer.kaiostech.com/design-guide/hosted-app
4.https://github.com/firegnu/kaios-hosted-sample
5.https://nolanlawson.com/2019/09/22/the-joy-and-challenge-of-developing-for-kaios/#comments