I suppose I should take this being the expert on 50 vine vineyards.
Your first challenge will be picking when the grapes are ripe. Grenache is really tricky because the grapes on the outside of the cluster can be shriveled and on the inside they are still pink. You’ll need to pull samples from inside the cluster to make sure everything is really ripe. You can buy a refractometer for $50-$75 (US) or see if someone might loan you one for 10 minutes. If all else fails, find a neighbor who makes good wine and pick when they do.
Next up is picking. Be harsh, be cruel, be tough. The number one mistake home winemakers make is using poor fruit. If it’s got rot, shrivel, fungus, pink berries, whatever, throw it out. The pros don’t think they have the skill to make something good out of something crappy, so don’t fool yourself, you won’t be able to either. Use only the best grapes.
Get some citric acid and sulfur. Whatever you decide to ferment in you’ll need to clean really well. For this scale operation, crushing isn’t really that important. If you have someone who will do it for you, or can rent a crusher then great. Otherwise put the grapes in your fermentation vat and jump in. Get yourself some Argon. There are lots of steps in this process where you’ll need to protect the juice and then wine from O2.
Fermentation should be easy for you. You can buy yeast, but I’d bet it goes on its own. If it’s your first time you’re probably better to buy though. Do your punch downs, and check your brix every day.
For you the hardest part is going to be pressing the must. This is really the point you’ll wish you had a friend with equipment. You can make due with various kitchen gadgets, but you’ll really wish you had at least a 35 gallon wood press ($500). After pressing you’ll need something to store/age the wine in. This can be tricky, and you’ll need the argon again for sure. You want to have enough to fill whatever storage device you use 100% plus some let over to refill the device as it evaporates.
The number two mistake home winemakers make is with sulfur. In general they add too much at crush and not enough later on. Keep that in mind.
That’s the 10 minute overview. I’ll tell you the best thing you can do though is find someone who you like who makes good wine. Say “I have 500 pounds of Grenache on my property, if you come take it will you give me back a few bottles when it’s done?”