Do I need an audio interface to use the Roland E-4?

No. It processes whatever you feed into its 3.5 mm aux input and sends the result out the aux output. You can plug it between a mic adapter and a recorder, mixer or computer sound card.

Can the E-4 replace a vocal effects pedal?

For desktop and streaming use, yes. It gives you reverb, delay, chorus, echo, vocoder and a looper in one small box. A stage pedal still wins on foot control and XLR connectivity.

Does it work as a USB audio interface?

No. The E-4 is an effects processor, not an interface. You route audio through its aux jacks and record with whatever interface or recorder you already use.

How long can the looper record?

The looper is short and meant for quick vocal layers and ideas, not full-song looping. Check the manual for the exact maximum before relying on it for performance.

You get the E-4 unit itself. Check the listing for the power supply and cable bundle, since some sellers include them and some do not.

Is it good for podcasting?

It can add reverb, echo and vocoder color to a podcast voice, but most podcasters want an XLR mic input and cleaner routing. It fits better as a creative add-on than a main interface.