variables size limitations

Question

I am pretty new to VB.net and actually programming in general. I am a geneticist with some background in webdesign and basic (very basic) C++ and am making an application for organizing gene sequence and other misc data. I've made a simple database application that will load a database and let an user update data by entering it into a text field. I understand that access databases have a 255 character limit for text fields. Is there a way to get around that?

If not, I plan to save long text data in a txt file and just store the path to that txt file in the corresponding table field. But I will need to manipulate the text in the txt file. What are size limitations for String variables? Would storing the entire text from the txt file in a variable be a good way to manipulate the text or is there a better way to do it? Would I be able to do that with a readstream or something similar?

Just as some extra info. The data I am storing is about 10,000 characters or more long. The characters only consist of 'A' 'G' 'T' and 'C's with no spaces. I mainly just need to be able to search within the text and be able to highlight certain fragments or change the color of certain fragments in a rich text box control.