"First, second, last" vs "first because, second because, last because."

When to use the former or the latter? Example:

I picked NTU Library. First, (because) it was my university's library, so I wouldn't have to walk very far. Second, (because) I liked the atmosphere. It was very modern. It had colorful furniture and shelves arranged as a concentric maze. Last, (because) it had the largest book collection in Taiwan, enough to fill a soccer field. At least some of them must have been about 3D printing.

Is the because-version adequate? Or it doesn't make any difference?

First(ly), secondly, lastly. In such sequences where points or topics are enumerated the choice of form as between first and firstly is optional in modern English. (Fowler's Modern English Usage )

In practice many different patterns are used:

• First, ... second, ... third;
• Firstly, ... secondly, ...thirdly;
• First, ... next, . . . last; (AmE)
• First of all, ... second of all, ... thirdly;
• and numerous others.

Burchfield, in Fowler's, has hit it: "Logic did not and does not come into it." Gowers, in the second edition of Fowler's (1965), says "The preference for first over firstly in formal enumerations is one of those harmless pedantries in which those who like oddities because they are odd are free to indulge, provided that they abstain from censuring those who do not share their liking.

Your "because-version" is grammatical, however, to me, it appears a little clumsy and wordy. I would keep the first "because".

Consider this: First(ly), because it was my university's library, so I wouldn't have to walk very far. Second(ly), I liked the atmosphere. It was very modern. It had colorful furniture and shelves arranged as a concentric maze. Last(ly), it had the largest book collection in Taiwan....

It is clearer with because, but there are many ways to write it.

An alternative is, for example,

I picked NTU's library for several reasons. First, it's my own school's library, and so only a short walk away. Second ...

You should probably use present tense verbs for statements that are still true. Is it still your school's library? Still like the atmosphere? You can keep wouldn't because it was hypothetical at the time you were deciding.

You should be consistent within a set of bullets, as it provides an emotional and logical continuance that the bullets belong to the same set.

• First, ...
• Second, ...
• Third, ...
• ...
• ...
• Last (but not least), ...

• Firstly, ...
• Secondly, ...
• Thirdly, ...
• ...
• ...
• Lastly (or, finally), ...

Imagine if people bullet their items this way
A. ...
b. ...
III. ...
4. ...
ε. ...
ה. ...
七. ...