1. What is the minimum amount that I can invest?
我最少應該投資多少？
還能這樣說：
How much can I invest at least?
What is the minimum investment?
應用解析：
invest in 投資于；投入；
invest with 授予；使帶有；使籠罩著；被……所包圍
2. We plan to buy a new property as an investment.
我們計劃投資買套房子。
還能這樣說：
We are thinking of investing in a new property.
A new property is our investment.
應用解析：
go according to plan 順利進行，按計劃行事；
plan sth. out 策劃或詳細安排……
3. They decide to participate in the financing of real estate.
他們決定參與房地產投資。
還能這樣說：
They make a decision to invest in real estate.
They want to take part in the investment of real estate.
應用解析：
participate in a discussion 參加討論；
participate in profits 分享利潤；
participate sb.'s sufferings 分擔某人的痛苦；與某人共患難
4. It's the best time to invest now.
現在是投資的最佳時機。
還能這樣說：
It is wise to invest now.
It's to your advantage to invest now.
諺語：
Wealth is best known by want.
人窮方知錢可貴。