Q1:what does "the buildup of the country"mean?
“Essentially. It doesn’t add up otherwise, not if you really dig into the expenditures, the revenue. Family lore says gambling—they liked to gamble and they were lucky. And they were smart businessmen. Then the war, the buildup of the country. All of that, yeah, but gamblers need a stake.”
“You’re sure it was the dowry.”
“It’s logical. I want Tricia to take a look, to analyze, and I want to hear back on James Fitzgerald. It adds up, Abra. It’s in the walls, the stone, the glass, the gables. They accounted for it, in their own way, Roger and Edwin, because they considered it theirs.”Q2: what does "all of that"mean?Q3: what does "need a stake"here mean?

Question

Q1:what does "the buildup of the country"mean?
“Essentially. It doesn’t add up otherwise, not if you really dig into the expenditures, the revenue. Family lore says gambling—they liked to gamble and they were lucky. And they were smart businessmen. Then the war, the buildup of the country. All of that, yeah, but gamblers need a stake.” 
“You’re sure it was the dowry.” 
“It’s logical. I want Tricia to take a look, to analyze, and I want to hear back on James Fitzgerald. It adds up, Abra. It’s in the walls, the stone, the glass, the gables. They accounted for it, in their own way, Roger and Edwin, because they considered it theirs.”Q2: what does "all of that"mean?Q3: what does "need a stake"here mean?

Answer

"The buildup of the country" - the increase in the power of the economy of the country, particularly after the war.
"All of that" - all the factors that the speaker has previously mentioned: Gambling/luck/war/buildup.
"need a stake" - in gambling - you start by gambling a certain amount of money. If you win, you can use the winnings to gamble again, and again. The initial money that you gamble is called a stake.