Hi, take a look at the Squarp Rample.
There are no samples duration limits, can play 4 mono or 2 stereo samples, support layers (think round robin or other creative purpose), you've got Fx and parameters under CV control.
If it's important for you to see the sample's waveform on a screen I would also consider an Erica Sample Drum.

"I would also like to store my own synth engines on it and control them via CV/gate"
do you mean importing a single looped cycle waveform?