You can buy new OS 3.5 / 3.9 from Vesalia in germany for example (
www.vesalia.de )
OS 3.5 is quite cheap there for 9.90 EUR
OS 3.9 is still quite expensive at 35 EUR, better go for the OS 3.9 and book bundle for 37 EUR
OS 3.9 would be highly recommendet, as it has some really nice improvement over 3.5, one point being a full TCP/IP stack and not just a demo as in 3.5
A mere 030 and no graphicscard will let you feel a serious impact in speed compared to a barebone 3.0/3.1 System but this is manly caused by better looks. While 3.0/3.1 WB usually ran in 4 or 8 colormode it is recommendet to use at least 32 color with 3.5/3.9, better 256, but that would really hurt on plain AGA.