TB6560 Single Axis 3A Stepper Driver

I bought 3 of these: [www.ebay.com]

I intend to use them with Arduino Mega2560 + RAMPS 1.4 + Marlin.

Are there other issues than getting 24V Power supply for these and increasing the Marlin's timing?
Do these boards as well have the slow optocouplers? If so has anyone modded to bypass them?
Also these boards also require first +5V logic supply and only after that Motor power? Any suggestions how to delay a relay or should i control this via Arduino somehow (lol hookup relay on cooling ping and enable constant cooling in slicing? )

Oh and i realize, these in itself will need a fan, most using that chip has way larger heatsinks. Or maybe i'll just replace with a old huge CPU cooler

The main issue with these chips is that they require a long step pulse. Marlin's step pulse is by default too short to trigger a step with these drivers. Teacup and Repeteir are pretty easy to get working with these drivers. You can find some discussion about the chips in the Sanguish forum thread. Marlin can be modified to work. I forget where I saw a fork of it, but I've seen someone claiming to have gotten it to run.

Also be careful about the power on sequence. You are correct that the 5V needs to be on and stable before motor power is applied. On Sanguish the sequence is enforced by a relay controlled by the power pin similar to how Gen7 controls ATX supplies.

The heatsinks are probably fine as is, up to 2 amps or so. With a fan I think 3 A would work too.

I've seen stuff about issues with slow optocouplers but I couldn't say for those particular boards.

The listing says 6N137 optocouplers.
These are fast couplers.