1 - Depends on the quality of the screen and the ease of controlling it's brightness. You can get accessory shades which help.
2 - Framing - what is shown on the screen is TTL and therefore in theory, it's the same as framing an SLR. In practice, I'm no great fan of TTL viewfinders, preferring to see a bit around the edges so that I can fine tune composition. Screens, I find, put one at something of a disconnect to the picture and therefore framing takes longer. It's personal taste but many better photographers than I manage so I hardly feel it my place to bitch too hard. As an aside, I'm hoping olympus will release another clip on vf, possibly like a russian turret one to work with the zoom at 14, 17,20/25, 35 and 42mm. Cat's chance I hell I suspect, at least in the near future, but hope costs little.
2b - Focussing. My only experience with live view mf was on a Panasonic FZ50. Took a few minutes to get used to but I found it a deal better than MFing an APS DSLR - though not a quick method. Growing up with MF SLRs with split screens and microprisms, it was a luxury to be able to make focus decisions again. I was hoping the lenses would have a DOF scale for zone focus......please olympus?
3 - Depends on your sunglasses. Get some with grey neutral density lenses if you want to be sure. Olympus AWB on their E1 blew everything else I've used to this day out of the water. That camera was released how many years ago for them to have improved it yet further? More important is glare. Depends on the screen - accessory hoods help though can look silly.
4 - that's your eyesight. not mine - I don't think any of us except you are able to comment!