English Grammar

1. There are two sentences, not one.
2. "Gonna": non-standard dialect informal; standard: "going to"

One might write: "After i've bought . . .

Indeed.

After I buy a lifetime supply of food, I'm going to isolate myself forever.

...forever! but only after I had (or have) bought my (or a) lifetime...

Oh okay thanks! The sentences I came up with now are:
"I'm gonna isolate myself from everyone else! After I've bought my lifetime supply of food."
I was focusing on the "After..." I was not sure in using "after I bought" because the event I am referring to hasn't happened yet. Thanks! I only added "'ve" to the I.

Model, that just doesn't hang together well, needs some sort of connection, like "But that's only after...."