I've only been using the FZ28 for the pass couple of months, so I'll try in my limited ways to answer some of your questions.
For straps, maybe you could just try adjusting the length? Personally, the original strap is ok with me. If you want to replace it with another strap, do make sure the width of the strap that is attached to the camera's strap eyelets is narrow enough. The strap eyelets are pretty narrow, and wouldn't house conventional straps made for DSLRs. But I'll rather keep it the way it is. Simple is beautiful.
Rather than wide angle lens, I think you are referring specifically to wide conversion lens. I don't use a wide conversion lens at the moment for I find the wide extreme of 27mm to be sufficient. However, do keep in mind that with any form of lens adaptations, there will be certain issues that we must be aware of (barrel distortion, degradation in image quality, possible vignetting...etc). Please refer to the good chaps in the FZriends Thread for some good advices. This is the link.
http://www.clubsnap.com/forums/showthread.php?t=465019&page=41
As for lens adaptor, there are a few set-ups to consider. The originals by Panasonic are DMW-LA4 (wide), and DMW-LA3 (tele), which are expensive. The Pameraal PA62E (
http://www.pemaraal.com/index.php?page=fz18ac), which is ordered from US, but can be expensive too. Or the after-market lens adapter tube commonly use, as shown here:
http://cgi.ebay.com/58mm-58-Lens-Ad....c0.m14&_trkparms=65:1|66:2|39:1|293:1|294:50
The Pameraal is good, for the length of the tube can be varied, to accommodate tele & wide converters; and filter set-up. However, price is a consideration.
The after-market lens adapter is comparatively cheaper than the originals and Pameraal. It is basically a 2-piece tube. You attach the base tube for wide converter lens. Or attached the other tube over the base tube for tele converter lens. Similarly, you can use this for filter set-up as well. However, the length is not varied like the Pameraal; which unfortunately, leads to other issues (another discussion on it's own, which I wouldn't attempt).
Depending on which set up, you may need a step-ring to accommodate the converter lens to the lens adapter. For example, using the third party adapter tube, I may have to step down from 58mm to 55mm.
Well, I hope this info is useful. Don't be a stranger, and consult the good people in the FZriends thread. They helped me tremendously when I got my FZ28. As to where to buy the straps, adapters... etc. It is best you consult them too, for I bought all of my stuff in HK.
Try and keep the set up as simple as possible.