The A1000 is a nice Amiga, but it's hardly realistic upgrading it in such a way running OS3.9 would be possible.
If you are planning on running OS3.9, you should choose an Amiga with better upgradeoptions. One of them is the A1200: can be found rather easy and not to expensive (although price seems to be rising), has the latest AGA-chipset and expansions like extra ram or turboboards can be found all over the place. The other one I would recommend is the A2000. Older than the A1200 and does not support AGA-software, but very easy to expand and can also be found very frequently for a reasonable price.
All other Amigas are either rare and therefor expensive (A3000D/T & A4000D/T) or much harder to expand (A500 & A600) and are therefor not a very good start for someone just wanting to start fooling around with OS3.9.
Nevertheless, the A1000 is a very cool machine, especially if you have some extra fastram with it (which is becoming quite hard to find, I must say). I don't have one and am also not planning on buying one, but wouldn't turn one down if it was offered to me for free...
