be aware that once your body has reached its muscle creatine threshold, then using more than 3-5g of creatine daily is not going to saturate them any further, so there's no point in using more than that daily.
Doesn't make a difference. Everyone has a muscle creatine threshold of between 150-160 mmol/kg dw, and once it is reached, it canNOT be saturated further!
Once your creatine muscle threshold has been reached ~2-3g per day is enough to maintain those elevated levels, with a bigger individual will use the higher end of the range and a small individual the lower end - for example, a 70kg (i.e. 154 pounds) individual has a daily creatine turnover of 2g (Burke, et al., 2006; Harris, Soderlund & Hultman, 1992); using this ratio, a 200-pound individual has a daily creatine turnover of ~3g, and a 250-pound individual a daily creatine turnover of ~3.2g. Therefore you can see that there is not a lot of difference in the daily creatine requirements of a 150-pound individual and a 250-pound individual, so no, a "bigger guy" doesn't really need a lot more creatine than a "little guy".
Regardless of how much muscle you have, your body's creatine holding capacity is 150-160 mmol/kg dw (Burke, et al., 2006; Harris, Soderlund & Hultman, 1992).
A larger individual will have an overall larger amount of creatine in their system than a smaller individual because they have more dense weight, but it will still take the same amount of time to build up that creatine muscle threshold (i.e. ~20g a day for ~5 days (saturation occurs after 2-3 days), or ~5g a day for ~21 days) (Burke, et al., 2006; Harris, Soderlund & Hultman, 1992).
Your total muscle creatine concentration can only be increased by ~20%, with ~20% of that increase in muscle creatine being stored as Creatine Phosphate (Harris, Soderlund & Hultman, 1992).
Therefore, you can see that even 5g of creatine a day is plenty adequate for the biggest of individuals.