Asking for help:
Q1: I have set my 401k contributions to 6% (maximum amount for 100% company match). Should I invest more?
Q2: I have no idea what a good investment here is. I have 70k on my checking account. Where should I consider investing this amount?
Q3: I bought a beater that eventually will require maintenance. Buying a cheap brand new motorcycle to commute would be a good idea to save money and avoid car maintenance?
Q4: A good house here costs $350k. Should I consider buying a house instead of renting? I am currently paying $1,400.
Q5:Anything else that I should consider?
I can't speak to the international aspects, but I can give some basic advice.
1. Yes. Your 401(k) is likely your best investment vehicle from the standpoint of saving on US taxes, and of course lowering your current tax burden leaves you more money to invest elsewhere. Whether it's the best option for you depends on the tax treatment those assets would receive in your home country, of course.
2. I am a fan of simplicity. You have a long time horizon and a good income, so you have a good base to weather ups and downs in the stock market. That means you can afford a high percentage of stocks. For simplicity, I'd look for a total stock market index fund or ETF. Basically, you want broad market coverage + low expenses, which for many of us here means Vanguard. I would personally keep a large emergency fund (at a minimum, enough to get you back home; preferably enough to tide you over while you work the visas and look for a new job, then get you home if you don't succeed), and then put everything else in VTSAX.
3. If you'd enjoy a motorcycle commute and that would serve in bad weather, then no reason not to get a motorcycle, or even an e-bike. But why not get a used one, like you got a used car? If the goal is to save money, then save money!
4. No. If you buy a house, you should view it as a luxury rather than as an investment. Sure, you might get lucky and hit one of those super-hot markets -- or you might run into something like 2000 or 2009, when many of us couldn't sell a house to save our lives. So if you're looking to buy to make money, I'd consider that pure speculation, not investing. The main reason to buy a house is because you want a nicer and/or bigger place to live. But in many, many parts of the country, it's cheaper to rent. So as long as your $1400 apartment meets your needs, why pay more to live somewhere else?
5. I don't know much about visas, but the O1 designation looks pretty limited, as it is founded on some special talent or ability. What is the likelihood that your particular talent/ability will remain high-demand for as long as you want to stay here? Just thinking practically, if you're something like a brilliant professor, then it seems likely you'd continue to qualify for years; OTOH, if you're something like a pop star, well, whatever your innate abilities, musical styles go in and out of fashion, so 5 years from now, someone could decide, eh, no reason to continue to extend the visa (this is all assuming you don't get permanent residency in the interim, of course). In addition, if your visa/employment depends on a specific talent, look very hard at disability insurance and/or other types of insurance that would protect you if you get sick/injured in a way that takes away that special talent -- for example, if you're a concert pianist and get in a car crash and break your hands badly enough that you can't continue to perform at the top levels.
IOW, don't just focus on the upside, but also protect yourself against the downside risks. You have a great plan to set yourself up for a very secure future, and it's reasonable to think that you will be able to execute that plan. But there are many, many ways even the best plans can go wrong, from car accidents to political changes to market meltdowns, etc. So it's worth spending a little time playing the "what if" game -- what are all the ways things might go wrong? -- and then taking reasonable steps to protect yourself in the event something like that happens.
