Nobody can address any of these?
I think we are in a transitional period and some of the questions will become clearer in the next few months. As of September Chrome will block Flash Ads, Firefox already has them paused so for Banner Ads HTML5 is going to be the way to go.
I'm hope other people will reply to this thread as I'm interested in what's happening next and peoples thoughts on it.
I'll try and answer some of your questions best I can with what I know at the moment.
1. My understanding is HTML5 works differently to Flash, the 40k limit will not be the same as when building an ad in Edge as you're using code in the browser and Java script.
2. This is true, it may mean for the time being having to taylor designs and work out where HTML5 has issues and where it performs well. I've noticed scaling images in HTML5 you can see issues that the smoothing setting for images in Flash would sort out.
3. I've found this can be true and you also see variations of the way text displays across browsers. Depending on the typeface or where it's coming from e.g. typekit or google fonts it can look ok. I've found scaling can be an issue, as it is in flash without having the option of anti alias for animation set.
4. This is true html5 won't be able to animate vector shapes like flash can. Maybe something that will be possible in the future. I've found you have to be clever in how you combine SVG shapes with html shapes sometimes layered on top of each other to get what you want, using clipping masks and symbols. I remember having to get a square rotate it and then clip it to get a triangle shape for example. Complex SVG will create more for the browser to do and I think it's better to use shapes in edge wherever possible.
5. For browser issues I think it's worth having fall back options, where you can set a down-level stage and things like that.
I'd ad to this there are also Google Doubleclick Edge templates if you use ad servers at all. Companies like Celtra look another way lots of people are using HTML5 for banner advertising. Google Web Designer is being used as well.
I forgot add a point about re-compression of images and working with PNGs.
Flash can separate image and transparency layer in PNG then re-compress the image layer as JPEG and reapply the original transparency mask to it, effectively creating a JPEG with transparency format.
For apparent reasons you can not have that with HTML.
In the short term I would use the Doubleclick Edge templates. DC has said that the larger file sizes that HTML5 requires will be permitted. I have DC Studio access and have uploaded a DC Studio Edge Animate template first banner ad practice file and there was no dialog warning about the k weight of the jquery script.
The DC Edge templates have DC's method of tracking clicks built in and call the DC enabler script in the head.
This is the build guide for using Edge to build ads for DC
If you don't have Studio access you just zip your publish web folder in order to deliver the ads..
IMO HTML5 ads are going to need third party vendor support for the tracking.
I was also impressed with AdForm and Flite for building HTML5 ads.
I'm currently getting to build HTML5 more for live projects now. I'm finding using things like... TinyPNG – Compress PNG images while preserving transparency from PNG24 saves from photoshop will give you good alpha channel PNG8 files which are much smaller. Or https://pngquant.org/