The best Toa for defeating Gurrahk (level 1) are Matoro for beating Guhhrahk Hajli and Jaller for killing summoned enemies.
Defeating Vezon
After you defeat all Piraka, you will have to fight Vezon for the last time. First hit him the back, then in the legs, then the heads, then Vezon. After that you can play as Vezon in all levels.
Easy Lego pieces
In the level where you fight Roodaka, go to her and hold X. After you get hero mode, use tape your controller to keep X held so your character keeps attacking. Use Hahli, Vezok, or even Vezon so that they keep shooting streams to easily defeat the summoned Visorak. Because of the auto-aim when there is a villain your character locks on automatically, kills them, then switches. Because your character in Hero mode is invincible and it is unlimited, you can gain easy bolts.
Completely upgrade Toa Nuparu at the Matoran Enclave shop. Collect 500,000 Lego pieces and buy "Bonus Level 1". Go to the Piraka Playground. Go to the other side of the playground. Once there you should find a cave/pathway between the Piraka VIP lounge and the Piraka diving board. Go inside the cave and there are three portals. Go through the first portal on your left. Once you are in, switch to Toa Nuparu and start destroying multiple enemies while collecting Lego pieces. Do this quickly, as you have a 112 second time limit. You can get an average of 50,000 to 70,000 pieces every time you try the bonus level.
Collect all the Lego bits in the Matoron Enclave then go to the Priaka Playground. Go back out. Keep doing this for a lot of Lego bits.