If this recording thing is something that's important to you, and you want to do it forever, this is what I think you should do, because I do it, and it works great and is simple to set up (hopefully I won't confuse myself and you): Treat the room. Get an out-board reverb unit and set it up in a rack. (I have a Phonic in the rack; a good unit, but impossible to find). You'll need to do this eventually anyway. Get a dedicated monitoring device, like the PreSonus Central Station. Put it in the rack. Get a patchbay(s) and put that in the rack. It appears your mixer does not have AUX sends and returns. It also is designed for stage work. Use it for that only. Get a mixer with AUX sends and returns, like the Soundcraft GB2R (pictured). You have the computer and the interface. It looks like that MOTU has plenty of outs and ins. Run the reverb unit's outs and ins through the bay. From the bay they go to the mixer's AUX inputs and Stereo AUX returns. This is straightforward; hooking up the bay to your various bits of gear adds massive flexibility to your rig. I see that the MOTU has a virtual mixer; I believe you can do further routing with that, but get the MOTU's main outs on the bay and/or Central Station. Determine the amount of cables you need, and the length, and hook it all up. Start out simple, and add cables and connections that you think you need as you go. The idea here is to monitor from either the Central Station or the mixer the combined signals--what's going in, and what's coming out. You can do it through the MOTU too, of course, but I'm not sure how flexible that is. NO latency, because you're using the outboard reverb to add treatment via the mixer that your monitoring the signal from, the stereo track and your new vocals. The dry signal ONLY of your voice (or whatever--I use it always on steel guitar, for instance) gets recorded, or you can record the reverb, together or separately. Lastly, get a Behringer ADA 8000. For the outs more than the ins. Put it in the rack . . . .
So, your voice is routed to the mixer, where you use the AUX sends to give the reverb unit your voice, and it returns it to the mixer via the AUX returns. You adjust the amount to taste. The computer is recording your dry, un-effected voice, simultaneously. As long as the MOTU has the functionality of routing inputs in real time to its outputs, you're good to go. I use an RME RayDat, but I think the MOTU will work.
So: I know it seems kind of dickish for me to declare "hook it up," but that is the way to learn how to do it. (Private message me and I'll give you a much more detailed look-in on how my system is set up. We can private message here, right?) It's actually pretty easy. You need to learn it. Why do it this way? There is never a latency issue. It's all in real time. You can record the reverb from the out board, or not. Either "attached" to your voice, or not, or as a separate track. It's in stereo, or mono. You can record through the mixer: the GB2R in question is a very good mixer, with great pre-amps, but I only use my Audient ASP 880, and sometimes a modded ADA 8000.
All of the suggestions above by the other posters will work for you; this is how I do it, and it is simple and reliable. You'll get used to it quickly, I can promise you that.
