After a look through the Core Rulebook and a quick Google search, I still can't find the standard for how many credits an 8th level character will have. How can I determine how much I start play with? 3d4*100 seems too low for a level 8 character.
It's a brute force calculation that isn't spelled out explicitly in the core rulebook. Short answer: 280K credits + max starting credits per class + (some) talents.
Long answer: Page 37 lists how much experience it takes to level. The Forumla for experience required to reach a new level is (currentlevel*1000). EG, leveling from 1 to 2 is 1000 exp. Leveling from 2 to 3 is 2000 exp (-sum of previous exp). From 3 to 4 is 3000 xp (-sum of previous exp). Etc.
Page 248 gives an explanation of experience gained per fight and the amount of credits each fight should award. Assuming you always have fights of challenging difficulty, it takes 5 fights to gain enough experience to reach the next level.
Page 248 also advises credits to be rewarded per fight on a formula of : average level * 2000 credits.
WIth some shortcuts, the formula for starting credits is = 5 * previouslevel * 2000 + sum of all previous levels. Or 70,000 + 60,000 + 50,000 + 40,000 + 30,000 + 20,000 + 10,000 + max starting credits based on class. Or 280K + max starting credits.