OK, most immigration firms are stand alone practice of immigration law. I can't recommend you a particular lawyer but If I were you, then choose either one of the:
1. Some, not all, are part of big multi purpose laws firm with a small immigration law office. In general they are not that greedy.
2. Some law firms are multi national offices (US and abroad) or multiple law offices (meaning several offices through out USA) of same firm.
Many good lawyers don't take any case as they want to take cases which can be successful. You have mentioned you are from Taiwan and I don't know how do you feel about Chinese people. In any major US city or any major US university has huge Chinese population and I am sure there are people from Taiwan too. You may want to contact some of those to recommend you some good lawyer. or you may want to pay a visit in person to see a lawyer and investment project in person.
No lawyer in his/her right mind will give you "guarantee" for any thing. It is your money at risk and your application at risk. If you are going to invest, just keep in mind this in general is illiquid investment and you can loose this money as well.
There is another immigration chat room
http://imminfo.com/ and it sponsored/run by a law firm and his main lawyer Ron Gotcher sometimes answer other people's questions on the chat room. May be you should try to ask your question there to get his feedback and some free advice or talk to him. I have not used that chat room much and I can't tell you how he is as I don't have any personal experience. I am NOT part of that law firm any way.
I think host of this chat room is also a law firm. If you look at the top of this page you will find his information as well. May be you should consider talking to him as well. In the past I have seen people posting good things about him here. Again I am NOT part of his law firm either so please do your own due diligence before making any decisions.