我去旅游的打算

(这）是我的第一次去越南，另外（也）是我第一次一个人去旅游。To indicate this travel, you need demonstratives like 这。And we usually put a "," after 另外, then we add 也 which means "also".

我觉的得跟朋友一起去是最好的，不过这次由于意外的理由（原因）所以不肯（可）能。原因 and 理由 in some occasions are the same, but here if you say 原因 will be more native. 

因此我决定了不用（住）宾馆更好，要不有可能我会觉得太隔离（孤独）的。用 in Chinese will be " use", but if you want to say " staying at a hotel or booking a hotel" ，住 is a better choice. Lonely will be 孤独. 

我预定了在一个民宿住三天，在会安. 会安有很多古老的建筑，还有不少沙滩。✓

我考虑过在那里试试骑摩托车，如果我可以克服我的害怕（恐惧）！克服 is usually followed with 恐惧， you can say 除去害怕，去掉害怕，but not 克服害怕。 

去会安以后我打算去河内，越南的首都。✓

我安排在年轻（青年）旅馆呆三天。hostel is 青年旅舍, a new trend in China. 

我很希望我的室友不是怪咖，其实我秘密的（偷偷地）想找一个驴友跟我一起去看河内的景点。偷偷地 it sounds more native. 

我也期望吃很多可口的菜，尽管(因为）我仍然戴牙套所以吃太硬的菜不行! 因为……所以……， unchangeable, it's used to explain a reason.  

我知道越南的pho又好吃又软，所以我能尽管把pho吃到饱 :D pho in Chinese is 越南粉.

The biggest of your text is the accuracy of the usage of every similar word. I believe that you can talk in mandarin fluently, and we can understand you. So my advise for you is to listen and read more, or you can watch some series made in China ( seriously I don't watch them at all), it will be a great help. Have a good trip to Viet Nam.