With the Rebel team, I don't think Nym is a very good choice - he's just not a very good 48 points, especially for the Rebels who actually have good cheap disruptive pieces like Juno Eclipse and General Crix Madine. I'd probably have a good look at adding General Crix Madine (if you have him), since he helps out Luke Rebel Commando, who you're already using. Personally, I think there are better melee choices that Relucian Warrior on Rancor and Obi-Wan Kenobi, but if you are going to use them, you should use a Twi'lek Black Sun Vigo to give them both Greater Mobile Attack. You'd also need some Mouse Droids (to spread Commander Effects round) and Ugnaughts (to blow up doors), and an Elite Rebel Commando or two would also be good.

So if you really want to play the Felucian Warrior on Rancor and Obi-Wan Kenobi, your squad could look something like this. I would have preferred to squeeze an Elite Rebel Commando in, but couldn't fit it, so it's using an R7 for override:
52 Felucian Warrior on Rancor
38 Obi-Wan Kenobi
27 Luke Skywalker, Rebel Commando
18 Twi'lek Black Sun Vigo
16 General Crix Madine
14 General Rieekan
12 Anakin Skywalker, Force Spirit
8 R7 Astromech Droid
6 Mouse Droids * 2
9 Ugnaught Demolitionists * 3
(200 points, 13 activations)

With other pieces, the Han Smuggler/Princess Leia combination is always solid, while you're probably better off squeezing in some Elite Rebel Commandos as your override pieces. General Dodonna is often a good choice too. If you want to run a big melee piece, I'd take Shaak Ti, Jedi Master over both the Felcor and Rebel Storm Obi.

Also, what kind of squad would nym go good in?

I think, at the least, you should drop one of the cheaper attackers, and bring in some more fodder like Mouse Droids, Ugnaughts, and R7s, so you have some door control and more activations. I don't think the Commander Effects of Mandalore the Indomitable and the Mandalorian Commander work that well together, so I don't think having them in the same squad is helpful, while they're both quite expensive for what they bring to the table.
- the Mandalorian Commander works well with pieces with a single attack (or a twin attack with no double) so they can move and still use all their attacks. It does works well with the Mandalorian Supercommando, as you've done.
- Mandalore the Indomitable works well with pieces that can move and then make all their attacks; like pieces with Greater Mobile Attack, like the Scouts, although sometimes the Scouts are better to sit back and make their attacks with Cloaked.

My idea of a good Mando squad before the v-sets looks something like this squad, which someone else made: http://www.bloomilk.com/Squad/68925/balanced-mandos

--balanced mandos--
26 Mandalorian Quartermaster
23 Mandalorian Captain
57 Mandalorian Scout x3
18 Twi'lek Black Sun Vigo
51 Mandalorian Gunslinger x3
8 R7 Astromech Droid
12 Mouse Droid x4
3 Ugnaught Demolitionist
(198pts. 15 activations)

The Gunslingers and Scouts are good attackers, and the Quartermaster and Captain help them out by upping their attacks and giving them twin. It's a good squad, and does really well against some things - the problems it has, which the v-sets have addressed somewhat, are:
i) A Lancer can just strafe through and kill everything pretty easily
ii) You can get out-activated easily by squads with tempo control, and you can get out-maneuvered since you don't have any movement breakers.