First CPA campaign

So it seems finally the time has come, after a lot of reading, videos, thinking, getting scared, trying other things, getting back to it I think I finally found the courage to go for it.

The network has good score on affpaying and I've chosen propelleraAds for the traffic (I hope naming involved parties is ok), the offer is a shopping app on the google app store for a tier 3 country.

Now the questions:
1. Being a CPI campaign (and being the app on Google Play), should I build a landing page? (Reading Charles Ngo blog, although he suggests to use landing pages 95% of times, he says he'd go without for one-click install/submit).
2. Is a tracker strictly necessary? (I read propellerAds has a very good reporting system and also something called SmartCPA which should help you, if not automate, optimizing your campaigns. In case I would opt for BeMod, thoughts?).
3. Which ad format to chose? PropellerAds provides pop traffic but has (recently?) introduced the new "native push notification" format, and I was wondering which format would be more suitable being the offer for a shopping app. (Or maybe this is something to split test as well)?
4. Finally the million dollar one, budget. How'd you suggest to setup the test campaigns and (approximately) how much to invest?

Thanks everybody, I hope to meet you on the other side (the brighter one)