Samsaran mystic past life isn't equally useful to all classes. In the case of a kensai magus, they don't have enough spell slots for a wide variety of spells, they can pick up some sorc/wiz spells via the spell blending arcana and the magus spell list is pretty practical for a magus anyway. True, mage armor isn't on it but you may be better to use a wand and UMD until you can get spell blending, you have so few spell slots.
That 3rd party ranger combat style works with either, or with a nature fang druid. A ranger has some more interesting archetypes available or a slayer has more talents. I think a slayer works better here but YMMV.
1: dirty fighting
Human: improved trip
Monk 1: IUS, combat reflexes
3: vicious stomp
Talent 2: trapfinding?
5: stick-fighting style
Talent 4: RCS 1 (power attack)
7: felling smash
Talent 6: RCS 2 (greater trip)
9: stick-fighting counter
Talent 8: rogue talent (weapon training) - weapon focus is necessary to get tripping twirl next.
11: stick-fighting maneuver
Talent 10: RCS 3 (tripping twirl)
You could take rogue talent (combat trick) at slayer 2 in order to bring the stick-fighting feats online earlier. Stick-fighting style then, counter at L5, maneuver at L9.
A nature fang druid can get big in order to trip huge enemies more easily than a slayer or a ranger (unless it's easy to buy potions of enlarge person in bulk in your world), and of course has full-on spells.
As a slayer? Str 14+2=16, Dex 14, Con 14, Int 9, Wis 16, Cha 7 seems practical.
If you're going to be drinking a lot of potions of enlarge person, the trait that makes doing so a move action could help. Bred for war is +1 CMB IIRC. Rough and ready might let you use a shovel or something as a quarterstaff and get +1 to attack with it. I'm sure there's others you could use, there always are.
A warpriest has feats stacked up to the moon and can increase the damage of the quarterstaff several ways so yes, certainly doable. I'd try for a 12+ Int because their base skills are so poor (Int 12, Wis 15 maybe) but it wouldn't be hugely different.
Human and still with the flowing monk dip, to L11? Maybe like this:
Human: improved trip
Flowing monk 1: improved unarmed strike, combat reflexes
WP1: weapon focus (quarterstaff)
3: vicious stomp
WP3: stick-fighting style
5: free!
7: stick-fighting counter
WP 6: greater trip
FCB 6: free!
9: stick-fighting maneuver
WP9: weapon spec. (quarterstaff)
11: lunge
Or like this:
Human: improved trip
Flowing monk 1: IUS, combat reflexes
3: TWF
WP3: vicious stomp
5: stick-fighting style
7: stick-fighting counter
WP 6: improved TWF
FCB 6: free!
9: greater trip
WP9: stick-fighting maneuver
11: lunge
Yes. I assumed you wanted the redirection ability. It should work just fine in heavy armor, as does the unarmed damage.
Edit: or not, if it's 1/day. Well, there's free feat slots in either build, you should be able to reshuffle things. If you like the way the feats come online fast then there are several options for a couple of bonus feats at L1.
I didn't notice either. Anyway, a staff magus. That isn't compatible with bladebound or kensai. You could combine it with hexcrafter if you wanted.
The staff magus is slightly inferior to a normal magus until 7th level and gets interesting from 9th-10th. Starting at 3rd you'd need to be patient. I think you prefer faster gratification?
Warpriest probably, with or without a 1-level dip for even more feats. Swift action spellcasting from level 2 is amazing and given a days warning you can come up with spells like remove blindness if they're needed.
Some variant on the warpriests a few posts above. More like them if you take some form of monk dip, a bit different if you don't.
Strength will be effective for you. War, glory and good are all blessings you could use too.
& yeah, none of the warpriest archetypes are especially good for this.
OK. What goal would you like to set beyond tripping enemies with a quarterstaff? If there's a certain image/description you'd like to match, or some abilities you'd like in particular, set them out and I'll see what I can do.
Tripping twirl isn't going to happen sorry. You won't get it before level 16 at best due to the BAB requirement, and 15 is as far out as you look IIRC. You can get something very like it with whirlwind attack - you can make trip attempts in place of normal attacks, you just won't get spellstrike on them the way tripping twirl allows. Unless you get tripping staff too, but I just tried and couldn't get that and whirlwind attack together on the same build in a good time.
So you can get whirlwind attack (attack and/or trip everyone adjacent) OR tripping staff (spellstrike when you trip someone), but not both, and not tripping twirl which is like both.
Stick-fighting style's chain and vicious stomp/hex strike are a couple more feat-hungry ideas it'd be nice to fit into this, and of course one of frostbite/rime spell or shocking grasp/intensified spell would be nice to have too...
Here's a couple different ideas.
Unchained monk 1 (this could be replaced with brawler or unarmed fighter easily) / hexcrafter staff magus X
1: dirty fighting
Human: improved trip
Monk 1: improved unarmed strike, stunning fist, combat reflexes
Staff magus 1 (L2): quarterstaff master
3: vicious stomp
Magus arcana 3 (L4): wand wielder
5: hex strike (evil eye?)
Magus 5 (L6): stick-fighting style
Magus arcana 6 (L7): maneuver mastery (trip)
7: stick-fighting counter
9: greater trip
Magus arcana 9 (L10): ghost blade
11: stick-fighting maneuver
Magus 11 (L12): piercing spell
13: persistent spell
Magus arcana 12 (L13): devoted blade
15: quicken spell
Or one without multiclassing
Human: improved trip
Staff magus 1: quarterstaff master
3: dodge
Magus arcana 3: arcane accuracy
5: mobility
Magus 5: combat reflexes
Magus arcana 6: maneuver mastery (trip)
7: spring attack
9: whirlwind attack
Magus arcana 9: wand wielder
11: greater trip
Magus 11: piercing spell
Magus arcana 12: devoted blade
13: persistent spell
15: quicken spell
Magus arcana 15: bane blade
For a hexcrafter bestow curse works with spellstrike anyway, and I can't see the attraction in making targeted spells like major curse work with spellstrike. Just cast them at the target and skip the roll to hit. Accursed strike isn't useful for any purpose I can think of. There's no need to change the arcana.
If you want tripping staff then you need to find 2 feats from somewhere, one with BAB +1 required (weapon focus), the other with BAB +6 required. You could drop whirlwind attack & its 3 prereqs to do so which would leave you with a couple of free feats at levels 5-7. you could get weapon trick (one-handed) perhaps, and maybe another improved maneuver feat as an option, or spell penetration, or get IUS and vicious stomp in place of both free feats.
Traits? There's nothing required or especially important for this in mechanics (maybe starlit hexer if you're OK with being a member of an evil cult; problematic at best), which means you can use them for the flavour that they're supposed to be for. Street wary and bruising intellect seem like they'd give your punk some street cred, or there might be something related to how he got started in magic, or you might get something related to ships, which you said might be a part of the campaign. If you like you can become a UMD expert, it wouldn't hurt.