As said, the techs are completely different, and you won't know what you need to research early in order to unlock a few essential techs by the time you need them, at least until you've played it a couple of times. I found the tech system needlessly complicated and tedious. The vanilla game is far more forgiving, and definitely has a shallower learning curve, not that its learning curve isn't already daunting enough for a lot of players.
As suggested, playing a major and learning the basics will at least give you some understanding of the core game mechanics, particularly how combat is handled, what modifiers do what, and what you need to do to win battles. The mechanics are somewhat different in BICE, but the information is displayed in the same manner, and many of the underlying principles still hold true, it's just that the numbers (and how to achieve those numbers) have changed.
Learning how to handle a minor country, and working with the mere pittance of Industrial Capacity (IC) and Leadership that you're given, may also provide some insight on how to make the most of what you have. It also gives you a bit less "clutter" to deal with, so you can devote a bit more time and attention to non-combat mechanics such as how to use Trade and Espionage as tools of diplomacy and warfare (note that the HOI3 manual is horribly out of date on Espionage and diplomacy, as they were overhauled completely in the later expansions). The HOI3 wiki has a lot of explanations and details, and is (or was) far more current than the manual.
Once you feel confident in your ability to play the vanilla game, THEN it's time to take on BICE. Personally, while I appreciate the talent and effort that went into it, and like many aspects of it, my overall opinion of BICE is that it's overly complicated, and excessively railroaded (it gives some extreme modifiers at some points, to force a historical outcome), and I just don't enjoy it.
