Help: Looking for good lenses for A40

[KOMR]

Hi,
I have an A40 and would like to get a Tele lens and a Wide Angle lens. However, there are many different kinds of lenses out there so I don't know how to choose.

Here are some of my questions:
1. What are front threads and rear threads? is larger the number, the better it is?
2. Are lenses with more mm always better?
3. Is the the aperture of a external lens very important? Are there any math I need to do?
4. I would like to buy the lenses that can be used on G2/G3 as well (my friend wants to use them sometimes). How should I manage the conversion?
5. does wide angle lenses do marco too?
6. What are the tradeoffs of large zoom/greater wide angle ability?
7. I saw these on ebay that are exceptionally cheap, what do you think?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1940708884
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1940351552
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=802729420

Finally, great thank for the help!

[MerdoQ]

Any commercial grade lens will fit perfectly the A40...since you do not expect to take professionnal photos with this 2meg cam ..dont u ?

[KOMR]

No, I am not taking professional photos.
Since I've heard that some lenses create blur and low constrast images, so I am looking for some 'average' quality lenses. not the poor quality ones and not the professional ones.
Thanks

[KOMR]

Does anyone has website links teaching ppl how to choose lens?
Thanks