Hi I was a SAF sniper PC during my NSF days. I'm not sure if you are dead serious about signing on as a snipper. My thoughts are
1. Yes, training is tough and so is the selection for sniper course. For NSF, it's more like they choose you rather than you choose to go.
Once you are in, it's very fun to go for range and live firing. Bn / Bde / Div level exercises are fun too, the only problem with the later is that there are way to few two-sided exercises. In camp, sniper life is good ... very good indeed
2. As for signing on as a regular (non commission officer), i feel that your army career is limited. You CANNOT stay as a sniper sgt for long. There are not many sniper regulars out that, most are "stuck" in sniper training wing (like a "sniper school"), converted to ops spec (S3 branch) or into the line units as PS, CSM etc. During my time, sniper platoon sgts were all regulars but now they are all replace by NSFs.
3. As for signing on as a regular (commission officer), you will start off in BMT, OCS and follow by sniper school. That will be more than 1 year combined. As with all regulars, your PC appt will usually last for a year or two, than you will likely have to move on to other non sniper appointments (unless you got backed back to sniper school). That's the end of your sniper stint. Sniper PC is a appointment not a vocation.
If you really like to be a professional sniper for a career you may need to join SOF or some similar outfit. Of course that's another story all together.