Should I play a "build" of a character my first time through in Diablo 2?

I'd recommend just playing. It will likely be more fun since you will be discovering as you go and building up the skills you enjoy (even if they aren't the most powerful), and many builds are likely min/maxed for level 99 with top-tier gear, something you are unlikely to hit at 3-4 hours a week.

Now that you can reassign your character's abilities, you can always re-spec to a particular build later on if you so choose. However, bear in mind that you can only do so once per difficulty without special items.

The answer to your question will depend on a few factors.

If you want to play through every difficulty or want to make sure that you don't inadvertently handicap yourself by choosing poorly, go with a predetermined build. I would recommend the Fishymancer for ease of use and simplicity for beginners.

Otherwise, take solace in forging your own path, bearing in mind that you may wind up wasting precious time out of your life if something goes awry. Also remember that you won't ever max out all of your skills. It's best to choose a 'theme' (as most builds already do) and stick to it.

Either way you've made a great decision to play a great game.

Have fun!

Most builds are designed with long-range goals, and optimized for high level play.

Between your casual play style, and the addition of multiple respecs, you're best off just going for assigning skill points as you see fit. If you find that what you picked isn't working well, you can always respec and improve.

However, you may want to look into some of the guides strictly for perspective on recommendations on attribute point distribution, as you cannot fix those later on, and a poor choice of how you distribute your attributes can severely impair your ability to play even at the mid-levels of the game.