Considering a project for an app that scans barcodes and communicates with a database

TL;DR - I want to make an app that will scan a barcode, then send a query to an online database. Is this possible?

Backstory

I'm thinking of taking on a project for my father, who is organizing a yearly hiking tour on the island where we live. They're thinking of modernizing the process of checking which participants have started and which have finished. Up untill this year, they did this by giving everyone a card with a number on, which is read to a volunteer at a checkpoint, who then checks them off a physical list. The idea is to switch to a system with barcodes instead. How this is actually supposed to work is what my father was trying to figure out when he came to me.

The idea

There are plenty of smartphone apps that can read barcodes, but for this purpose it needs to be possible for multiple people with scanners to 'check off' people from the same checklist (database) simultaneously. Because of this, I was thinking of making an (iphone) app that uses open source barcode scanner code to read the barcodes and then an internetconnection (3G) to access and update a central database. The aim for this year is 1000 participants, so that would be a list with id's from 1-1000, names, and 'status'. Statusses would be 'not started', 'started', 'finished' and 'dropped out'. You'd scan a code, then press a button to have the app send a message to the database to update that specific numbers status.

Questions

Firstly, I'm thinking of an iphone app because we can have volunteers use their own phones, but is that reliable? Would we be better off shelling out for a couple of handheld-scanners and using a pc with internet instead of a smartphone? The upside of being able to use smartphones is that as long as you have 3G conection, you can use it anywhere on the fly.

Secondly, is this setup of 'barcode-->app-->internet--->database' doable? I haven't worked with iphone apps before (I have a windows pc so I'd have to install OSX on a virtualbox). Also, does something that does this maybe already exist?

Thirdly, I'm not experienced with making apps, is it possible to make this and distribute it to a handful of people without putting it on the app-store? Like maybe physically connect the phones to my laptop and put the app on there?

Thanks for taking the time to read this, I really appreciate it!