I haven't played fighting games in a long long time (and before was never serious). Anyways, one of the hurdles I'm trying to climb is attempting to put together a team for KOF, so here are some of my questions:
Why did you pick Robert over Ryo? Is there any character similar to Chris from '97-'98? And when forming a team, is it better to diversify (ex: grappler, zone, balanced) or just pick what appeals to you?
This is an interesting question, but for the sake of accurately answering it, I have to ask some questions as well (or rather, you have to ask YOURSELF some questions).
What is your GOAL when playing KoFXIII? Why are you playing this game? How good are you trying to get? Do you plan on being a COMPETITIVE player?
If you do not plan on entering tournaments, then play your 3 favorite characters in any order you please. It's as simple as that. Having fun is the most important thing.
However, if your goal is to be competitive, then there are a variety of issues to consider. First and foremost, which characters appeal to you? Try playing these characters first. Learn them DEEPLY. What I mean by this is, learn AND PRACTICE the various combos you need to know, as well as the nuanced situations in which your moveset is useful (practicing setups and multi faceted offense is essential). To be considered competitive in KoFXIII, it is ESSENTIAL to know an optimal meterless BnB (both midscreen and in the corner) as well as the most practical meter using combos for each character you play. I recommend learning the optimal 1 bar 1 drive, 2 bar 1 drive, and 2 bar HD combos for every character you decide to play. Learn the best normals used in hop offense. Learn the best anti airs. Learn the most optimal hit confirms. This takes many, MANY hours, and cannot be done unless you play against real people for an extended period of time. AFTER you learn all of this, ask yourself two things:
A. Do I still like this character?
B. Can I WIN with this character?
If you answered no to either of these questions, drop that character. Drop the character, and don't look back.
Although this may sound harsh, as a competitive player it is a massive waste of time to play a character who you feel is a burden. As a competitive player, your goal is to win. If you feel that your character cannot win, YOU ARE DOING IT WRONG. Keep in mind that I'm not saying you should just "pick a top tier", but rather that even good characters just might not suite your play style or mentality. For example, Duo Lon can be a really scary top tier character in the right hands, but if you aren't the kind of player who can utilize his style of play even after tons of practice, then in your hands he's garbage, and it probably isn't worth it to play him. AS A COMPETITIVE PLAYER, IT IS IMPORTANT TO PLAY THE CHARACTERS WHO YOU BELIEVE WILL BRING YOU THE MOST COMPETITIVE SUCCESS.
It is also VERY IMPORTANT to note that there is a HUGE difference between losing because your character is bad, and losing because YOU are bad. Sometimes this can be a hard concept to really wrap your head around, but always ask yourself if you are losing because of glaring character weaknesses, or (more likely) because you fought someone who is straight up better than you.
To answer your questions specifically, I picked Robert because his normals are awesomely suited to my playstyle, he has a taco crossup, a command grab, and he's a badass. I never put in the time to learn Ryo, he never appealed to me (but I still think he's a very competitive character). I have never played Chris in any KoF game, so I cannot answer this question directly. I will consult other players in the community for you to see if they have any suggestions.
Diversity of character types on a team does not matter at all. I know a few strong players who play K', Kyo, and Iori as their team. Although I think this is very lame and boring (lol), it works for them. You can even play Raiden, Daimon and Clark on a team if you know how to do it properly! One thing that is very important, however, is TEAM ORDER. This is because your first character is limited to 3 meters, and your second character is limited to 4 meters. Because of this, you will find that it is more practical for your second and third characters to use meter rather than your first character. The implications of this are nuanced and depend on your specific team composition. It is your responsibility to determine the best uses your characters have for meter, and then to order them accordingly.
I hope this was helpful! Let me know if you have any more questions!