Interesting character; I would caution you to read Making the Tough Decisions, particularly Decide to React Differently, before playing (actually, I recommend your whole group read it, as it is excellent advice). You have a fun, quirky character, but you are responsible for that character, including the character’s quirks. You should not be ruining the game for others just because your character is quirky, and that means that you have to be able to justify your character participating in the quest despite these neuroses. It’s not actually that hard, but it’s important to keep in mind that it is your responsibility to do so.
Spear or polearm fighter
Reach is a very desirable thing to have, so this is a decent choice. Recommended for a fighter.
I want to poke, trip
Solid enough option for a fighter in Pathfinder, though sadly (and, I would argue, very much unnecessarily) badly nerfed from 3.5.
You will want Combat Reflexes, Improved Trip, and Greater Trip. The last two require you to have Combat Expertise as well. From there, Fury’s Fall lets you add Dexterity as well as Strength to trips, which is important because people add both to their defense by default, so it evens you out on that, plus you need decent Dexterity for Combat Reflexes.
You will need decent Dexterity and Constitution, and a high Strength, as well as an Intelligence of 13. Weapon of choice is a guisarme, a type of polearm, which corresponds well with your desire to have a long stick to poke people with.
If you look at the Feat Tree, you can find a (lot) more feats, some of which may be good choices. Not a whole lot left that works with trips, though. Of the feats that focus on tripping, Felling Smash is a trap, Felling Escape is pretty niche, and the rest either work with Unarmed Strikes or with Quarterstaves only. Considering your character concept, Felling Escape is probably fitting, so I might pick it up for that reason, but it would definitely be a very low priority.
A shield seems to make sense
Not going to work with the polearm; polearms require two hands and won’t let you use a shield larger than a buckler (and the buckler only works very poorly with a two-handed weapon, since attacking with two hands means you cannot use the buckler, but the buckler still gives you a −1 to attack).
At any rate, shields are fairly lack-luster in Pathfinder. At very high levels, a magic buckler may be worth the −1 attack penalty just because of all the magic it has on it, but aside from that I wouldn’t bother.
Does an elf make sense?
No, not really. Elves take a penalty to Constitution, and you’re talking about a mainline warrior who is looking to get in people’s way and trip them up. That’s going to draw attention to you, and you’re going to need to be able to take that attention. A penalty to Constitution makes that harder, and most of the best features of the elf (automatic searching, free weapon proficiencies) aren’t going to matter much to a fighter who doesn’t have a lot of skills and already has all of the elven weapon proficiencies. The bonus to Dexterity is nice, but Dexterity is a distinctly secondary priority after Strength. Fury’s Fall improves that, but even then you can get a bonus to Dexterity without taking a penalty to Constitution (and even then, Strength is still a bit better).
Could you play an elf? Probably. But it’s not the best choice. I’d probably want something with a bonus to Strength and no penalty to Dexterity, Constitution, or Intelligence (since Combat Expertise requires Int 13).
Is there an interesting, playable build here?
Sort of. It’s a good build for a fighter. It’s relatively reliable, forces your opponents to deal with you on your own terms more than most, and allows you to provide added value beyond straight damage. You’ll be able to stand in the middle of a fight and try to decide who gets to go where, at least within your sphere of influence.
That said, Pathfinder is not a balanced game; characters with magic can badly outclass those who do not. As a fighter, you will have to choose carefully, because your choices generally cannot be undone and you will have to live with them. Most spellcasters get to change their spells every day, and besides that they get way more spells than you will feats.
Moreover, because they have so many spells, spellcasters will always have something new to do – you will not. You’ll get better at tripping, might pick up another trick or two, but mainly, as a fighter, you have to pick your specialty and stick with it. Trying to generalize tends to leave you with a bunch of tricks that rarely if ever work against things of your own level. One might therefore say that the character is less interesting, mechanically, than a spellcaster, because you’ll tend to do a lot of the same things over and over in combat.
Of course, if everyone is new, that means that people won’t know how to make the best use of spellcasters. If they prepare the same spells every day, they aren’t getting that versatility that is both such a huge advantage and what might make them more interesting, mechanically. They might even choose so poorly that you’ll overshadow them; if they focus primarily on direct damage, but don’t do it right, you’ll probably be better at damage than they are.
But they don’t necessarily have to know the tricks for the reverse to happen. Sometimes new players get “lucky” and stumble upon very-powerful options. And because they are fundamentally more powerful, the odds of them being better are probably pretty good. It’s far from guaranteed, but there is a very real chance that the druid can do everything you can, but better, while simultaneously casting spells.
There’s also a risk that a new DM won’t recognize that certain enemies are completely immune to anything you do, and accidentally sideline you. While there’s certainly fun to be had even when you cannot directly contribute to combat, if it’s a regular thing it gets old really fast. Still, if that happens a quick chat with your DM after a session will probably clear it up, assuming your DM is conscientious and willing to work with you (and if not, you have bigger problems). But something to watch out for, especially at higher levels.
Speaking of, tripping is very much a low-to-mid level trick. At higher levels, magical movement modes become very common (which often prevents tripping), and in any event Combat Maneuver Defense tends to scale faster than your Combat Maneuver Bonus so it becomes harder and harder to trip things of your level. Unfortunately, most other mundane warrior tricks run into a lot of the same problems. Most new players tend to stick to fairly low levels because it’s simpler, so this probably isn’t a worry for you, but it’s worth being aware of.
Is there an interesting, playable character here?
I just wanted to say that, by this metric, you’re doing much better. Even if fighters are a little boring, mechanically, you have a very interesting character concept that should provide entertainment, if done well, for the entire group, even if he struggles in combat.