3 Gallon corny keg- purging, sealing and dispensing with CO2 dispenser

I have a 3gallon corny keg and CO2 dispenser and I had a couple questions?

The dispenser has no Co2 regulator and I'm trying to figure out how to operate the CO2 dispenser.

Proper purging? Fill corny keg with beer, close lid, lock...inject co2 with outake valve open to purge? about how much? Is it really essential to purge oxygen from a keg? you usually don't purge oxygen in bottles (I understand there is a lot more oxygen left in a keg than a bottle)

Seal? After purging should I close outake valve, and then blast a little CO2 in? In using CO2 dispenser how much of a risk is there of shooting to much CO2 at once and blowing the seals?

I'm keg conditioning this beer.Can I leave the CO2 dispenser attached for the 2-4 weeks while I keg condition? Will the CO2 canister last that long?

Thanks for your input everyone

How big are these co2 canisters? If they are the standard 12g or 16g carts, you probably don't want to force carb with those...they are really only for dispensing. Even if you tried force carbing with them, you'd go through a ton of carts and wouldn't really have a ton of control over the carb level.

I've done the very thing you describe with my 3 gallon kegs in the past (assuming you are using the 12-16g cartridges mentioned in the post above). It doesn't hurt to purge the O2 at all, and it'll give you peace of mind that the keg is sealed.
What I did, gently rack to the keg, close the lid, and hit it with the CO2 with a 1-2 second blast with the relief valve closed.
Pull the relief valve to relieve all of the pressure.
Hit it again with CO2 (1-2 second blast).
At this point I'd decide if I had enough CO2 left in the cartridge to pull the relief valve and seal it up again. You'll have to judge yourself based on feel. If this is the first time doing this, you'll probably use more than one cartridge - consider it a learning experience.
I think if you stick with the 1-2 second blast, you won't trigger the PRV, I never have.
Assume the dispenser is a one time deal, it'll leak out over the course of weeks, so I would not leave it attached for that long. Use it to purge and then seal, then take it off.
Put it back on later (with a new cartridge) to dispense if you need to.

I would recommend one of these if you're going to naturally carb in the keg. Let it get to about 30 psi at room temp (70 degrees) and it'll be good. If it climbs above, just relieve some of the pressure. You can use the same amount of priming sugar you use for bottling with this method, just make sure you bleed anything off over 30 psi. Let it stabilize at roughly 30 psi, and then chill it down. It'll take 2-3 weeks just like bottling. Keep in mind, if you do monitor the pressure with one of these, it'll be high at first from the initial seal, then it'll drop as the CO2 gets absorbed, then it'll climb again as the pressure builds.

Oh, and with the method I outline above, assume you'll use one cartridge every time you purge/seal a keg (so use the whole thing).

Also, with the bleeder valve, you'll need a threaded gas disconnect too. I don't keep mine attached to the keg either, I take it off after reading the gauge. Mine has a slight leak at one of the threads, not enough to bother with, but enough where it would depressurize the keg if I left it connected.

Yes I have 16gm CO2 canisters.

I do not plan to force carb this beer. I am "keg conditioning"
regulator looks like a good idea. What if I don't regulate it? any chance of a really bad outcome ie. exploded keg?

I'm getting into kegging but am kinda budgeting my way in- also im kegging this beer and then going on vacation for 2 weeks so I would not be around to regulate...bad idea?

its no biggie - keg condition with priming method of choice - in this scenario the little canisters are strictly for pushing the beer out - so you just it a hit of co2 and then pull the faucet, when it starts to slow to an unacceptable level, you hit it again... it's much like a hand pump in that regard.
not very hard, but also lacks consistency of pour as it will always be slowly decreasing pressure until you hit it again.

That bleeder valve isn't really a regulator, just a gauge, you'lll have to regulate it on your own. If you're not there for 2 weeks, it'll probably be perfect. I doubt it overcarbs in those two weeks. You won't have an exploding keg. The pressure relief valve would go before that, the poppets probably would too. Don't worry about the keg exploding at all. If you can spring for the gauge, I would, especially if you think this is a method you'll use for a while. It made me feel better to know what pressure the keg was at. Not so much because I was worried about safety, but because I liked to know when the carbonation was complete, and what level it was at.