If your compressor clutch kicks in, even for just a second when you turn the AC on you're in good shape. Means there's still some refrigerant in the system and it probably just needs a charge up. The refrigerant shouldn't leak out at all but it often does. Where it leaks from it normally leaves oil as it is carried with the gas. If you lost gas check all the connections to see if you can see an oily mess on one of them and that will be the leak. You can verify it with soapy water, and look for bubbles.
Replacing all the parts is as simple as unbolting the old ones and putting the new ones in their place. But if you do that or have to open your system you're going to need a manifold gauge and a vacuum pump. If it's just opened up for a moment to swap out the orifice tube you can just purge it by letting some gas through to force out any air, which is what I did. You could also replace the parts you need and go to an AC shop to have them evacuate and charge the system for you. The refrigerant charge should be under the hood on a sticker, or on the drier if it's the original. Mine takes 3lbs refrigerant. Be glad to answer any questions I can if you have any.
I must do mine before it gets hot too. Been a bit sick lately and the maintenance jobs are backing up. When I do it I'll take pics as I go. Here's the parts list for my truck
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$350 is still a lot of money, but I was quoted almost $200 from a shop just for refrigerant recovery. Thankfully if I wait long enough mine will completely leak out from the compressor. At a guess you're probably looking at close to $1k for a shop to do a complete overhaul.