.. wondering whats the best site to play with this balance.. or do i just need to add more to it just to be safe?
I recommend to you to exchange 100k satoshi in dodge coin and play dice game in fortunejack. You will generate huge amount of dodge and i see that having huge amount of capital is much lesser the risk you have in rolling dice but dont be too greedy like what they said there is no safe way on playing in gambling.
More capital = less risk? How could you say that? Logically the risk is always equal no matter how much your capital is. It is also not good to exchange his btc to doge first, unless his btc is on an exchange site already. He can just send the btc from his wallet to any sites as current tx fee is cheap.
Better to choose a site with low minimum deposit and low minimum withdrawal or even with no withdrawal fees. So it wont affect his small winning (if he win).
Is there a site without withdraw fees? 100k satoshis is 1 mbtc, almost nothing for dices. Probably the higher amount you have gives you more space to play martingale, but more money doesn't mean its more safe, I agree with that.
There isn't strategy for making a lot from just 1 mBTC, its a luck, play random bets, avoid martingale with that amount, bet low and when you think the next number will be some low one bet more on low, and try to catch some high bets with high odds.
If I can suggest nitrogen have one withdraw in two weeks for free, nitrogen have dices but maybe he can start with betting on sports, that is better for start I believe, and he can place minimal bets 0.1 mBTC. It will be easier to make money on sports betting then with dices.