I started of with a QUAD opamp, a TL084, then went to two dual opamps, TLO82's.
At 40Khz I was getting WAY too much cross talk between channels.
For the record it's not trivial, but it really isn't hard.
The main issues here is use multiple stages of gain instead of a single high gain stage.
When using a DUAL SUPPLY opamp you need to remember to supply biasing, thats what I've done with the voltage dividers on the positive input.
Don't try and build a non-inverting amp, go for an inverting amp, you should be able to adjust your biasing with a decent meter.
One thing I can sugest is get an old analog CRO, don't spend hundreds on a DSO, you will learn a lot just messing around with opamps and a decent 10-20Mhz CRO.