Want to make sure I'm legal with the build (tactics) I'm planning out with my animal companion for my hunter. (Have never played with a animal companion and want to make sure I've done stuff correctly)
Here's what I have so far for my companion (@ 4th level, stat bump to INT) -
Animal Companion - Tyrannosaurus
Feats: Acrobatic; Weapon Focus: Bite; (Outflank, Pack Flanking, & Precise Strike (class ability))
(HD 4; BAB +3; Fort +4, Reflex +4, Will +1; Skills 4; Feats 2; Tricks +2; Link; Share Spells, Evasion)
Skills: Acrobatics 4+2+6 ; Perception 0+2 
Tricks (7): Aid; Attack x2; Down; Flank; Guard; Second Chance Strike (Skirmisher, Immediate, misses with melee may reroll with -5 penalty); Aiding Attack (Skirmisher, Free, use on a hit - next creature to attack gets a +2 circumstance bonus to hit)
Tyrannosaurus; medium; 30' move; Low-light; Scent
STR 15+2 (focus), DEX 17, CON 10, INT 2+1 (3), WIS 15, CHA 10
HP 18 Fort: 4  Reflex 4+3  Will 1+2 
AC 19 = 10 +3 dex +4 natural +2 Natural armor (companion) Bonus
+8 Bite 1D8+5 B/S/P +1D6 precision damage if flanking with Hunter
+12 if Flanking
This has to follow PFS legal rules
First question: Are my hit points correct?
4 HD at 4.5 health per hit die, no con modifier.
Second Question: Tactics - Legal or Not?
T-Rex makes a attack, attack misses. Using the Skirmisher Trick Second Chance Strike as a immediate action makes another attack with a -5 penalty. This attack hits. Then using the Skirmisher Trick Aiding Attack as a Free Action the animal companion gives the next creature to attack the same target a +2 circumstance bonus to hit.
Third Question: Skills - are my total skills correct at just 4 skill ranks?
Forth question: Anything else I've done wrong/forgotten?