Thank you @Zhadow45 and @dpaterso for a great indepth discussion of this issue. That is quite a rarity for a forum!
Negativity and realism are very easily confused. I consider myself a realist and I guess I can often come across as negative because I am used to assessing the pros and the cons before making decisions. But that is probably the result of a lifetime in banking, primarily in risk assessment! 
In response to the actual topic of this thread, I don’t think the issue here is just how much money you have in your trading account. As a full-time trader one knows the type and size of one’s positions needed to achieve the quantified required/desired level of income. And one does not need to carry in one’s trading account more than the margin requirement plus a generous addition to cover the extent to which positions may go against you. Anything else is surplus in your trading account.
But that is not the whole story by any means (my opinion anyway). Everyone knows that trading income varies according to market behaviour and one’s performance. There are good months, average months and bad months, too. There will also be longer periods of both good and bad. Therefore one also needs a good deposit in some other place and form that can cover you over these periods and thereby avoid serious stress situations that will destroy your concentration.
In my opinion, this reserve should be sufficient to cover your living costs over a period of even up to 12 months without trading income - and still not leave you bankrupt at the end of it if you actually end up using it all up.
It is also worth considering when deciding how much one needs to earn, that this should also include a healthy contribution to your capital build-up. As you reach the autumn years of your trading career you will want to see something more for your efforts than just the fact that you covered your expenses and survived!
You will also need to take into account when projecting your income requirements that you will not be trading more than maybe 10 months of the year and maybe only 15 days of a month.
It is also relevant to consider whether you will be trading short term or long term. You will need to draw money to live, but long term trades do not always produce regular profits. Short term trades bring in the money but can be far more erratic.
These things need to be practiced and experienced and producing a track record before going full-time.
But the actual sums required depend on the individual and their commitments and ambitions. You don’t get inflation-linked or length of service-related pay increases and you won’t get pension benefits. You are your own boss and the result of your own decision-making - that is the benefit and the risk of such a business.
