Is there a botlane matchup you actually look forward to?

Take Fleet Footwork and Doran's shield; your early levels are rough because your range is one of the shortest for ADCs at that point. Try to only last hit as your E will push the wave automatically for you. I like to toss E on a low minion and AA it once to kill it when there's an enemy next to it because it actually has a lot of damage. You generally want to only go in when your support engages; be aware of the minions because jumping into a huge wave will fuck you up and you won't be able to get back out without fully charging your E on an enemy champion or if they die. The best combo is to E someone, land on them with W(it slows and stacks your E one time), and then orb walk with them with AA's to finish charging the E. When you hit six, you can use your ult to finish the combo as it will also give you a single stack of E and it does decent base damage.

Your match ups are only really as good as your support is. If your support is bad, you're going to struggle as your low range and inability to reliably trade early(E is a long CD, takes a lot of mana and has the counter play of, oh they walked out of my AA range; at one stack it doesn't do very much at all) means that you can be bullied out. However, if you're support is good and sets things up well for you via poking and trading or via CC(honestly Tristana likes having high CC supports like Thresh or Blitz is even better as he pulls people to him), you're really good at all in's.

Honestly, relaxing and farming through early is not the end of the world. If you go just even or even a little ahead with farm, you can scale reliably. That said, your midgame is bad because you don't have any abilities for poking and your AA's don't hurt yet. If you go into midgame behind then you're really screwed.

Think of Tristana as like an assassin; you want to win early because your mid is bad. If you fall behind early, you're just gonna be chasing around trying to catch up. In fact, Tristana plays very similar to an assassin early game and late game she's more traditionally ADC. Midgame, she's just garbage though.

If you feel confident though and think your lane will be easy(very few will be but if you get good, sure) you could take PTA instead; she stacks it fast with her Q and it does really well with her E because 3 AA's nearly fully stacks the bomb so on the fourth it gets a ton of extra damage. But only if you're confident.