They're really hard, I'm not going to lie and Matt Pederson can be a real a$$ if that's who you're looking to for advice. He's nice as pie until you have one that dies, that he'll treat you like garbage, so know that up front if you're going to venture into this.
I've kept a couple. I'm quiet about it on forums now because MP searches "Orange Spotted Filefish" in google for new threads about them and comes in and throws his weight around. Try to find a specimen that is already starting to eat frozen unless you really have a lot of time to devote to them. They are coral (SPS) eaters and that's what they live on in the wild. If you can get one that has already started to convert, you're way ahead of the game. It is very, very hard to find one that is converted.
I've converted one and bought one already converted, and the difference in the two was like having two different species.
If you're going to convert, make sure you have lots of SPS frags. Mine preferred encrusting Montipora to any other. They're finicky about water quality, so daily water changes work best. I had mine in a 14G and did 2cup water changes at least once a day. Offer small feedings often and be sure you have the time to sit and watch the fish eat. I've had a couple that would not eat if they knew I was watching, so you might have to hide. It really helps that I'm home almost all day and when I leave, my husband comes home, so someone was already around to tend to them.
While converting, some use a gel food and smear it on coral skeletons to get the fish to start to like the taste of other foods. I did not use this method. I would turn off flow and place mysis shrimp and brine shrimp in the branches of dead SPS colonies or half dead colonies. Both methods have worked for people and I suggest trying both.
The big thing with these guys, is that you have to be prepared if you can't get them to convert. Are you going to have enough SPS to supply for them forever? I was putting in 3 new 2" frags weekly and rotating frags out to get them to grow back for the next change.
They are an amazing fish, but you have to be very observant with them. If you're a feed and go person, it's not the fish for you.