Busy day today so I didn't get a chance to read through this earlier. I'm going to try to discuss a number of points that came up in one post.
How is it paid? I think it should be a monthly or biweekly check. I think most people are capable of making decent decisions on their own, and that it's demeaning to force people to spend in specific ways. As Dari mentioned, if you blow your GBI and your children are hungry, you have abused your children, and foster care for the children, and either prison, or my preference being moved to a halfway house and required to go through counseling and education for being a responsible parent.
Similarly for people who have substance abuse problems, or mental illness. One of the advantages to GBI is that when a person needs mental health care they bring with them a decent amount of money to help pay for it. I further think that savings in the prison system could be diverted to increased funding for mental institutions and substance abuse recovery.
For the PPP - I would actually be for a flat rate over wide geographic areas (at least at the state level.) The problem I see is that very desirable places to live like SF suffer from inflation because the area is desirable, if the GBI payment rises in those areas, it increases the desirability, and hence increases the inflation.
Where I see an advantage to the GBI system is that it becomes far less of a risk to move away to a lower cost area; you're guaranteed to have money when you get there, instead of worrying about finding a job. This has a bonus effect of bringing outside funds to lower cost areas, which are generally also areas with less economic activity, by adding people spending their GBI to those areas the economy will improve there. This adds jobs in currently depressed regions, and could help stave off Detroit like problems with a spiral of exodus.
I would support dropping minimum wage requirements, since everyone has basic living covered any amount of money earned over that is adding to their life. But at the same time by having a basic income level the need to work to survive is taken away, so people will be far less likely to work for overly low wages. This helps even out the power imbalance that naturally exists between employer and worker. I would strongly suspect that for the most part wages will settle to an equilibrium near to where minimum wage is; because if the work doesn't pay enough to really improve life it's not going to be attractive enough to get people.
On inflated prices reducing the effectiveness of the GBI. Given that there the fraction of the population that is at starvation level is quite low in the US, we are already spending the money for basics for the poorest to survive, for the most part for that segment this will be a change in how the funds are distributed, but not a change in how much is being purchased. So the overall effect on prices for essentials should not be changed significantly.
On immigration problems. Fortunately quite some time ago a country was faced with wanting to provide some security to people in the society, a sort of social security system. Of course they realized that just putting piles of money out for anyone to grab would be a problem. They hit upon a brilliant plan whereby citizens and permanent residents could obtain an identification number that would indicate they were eligible. Without this so-called social security number one could not receive benefits.
I recommend we hijack this idea with a GBI number only provided to citizens and permanent residents.