Memorization really is the key.
I took Latin for 7 years, including high school and college, so I know what I' talking about.
Memorize the five declension so that you can literally rattle them off in your sleep. That's just nouns.
Then, memorize the conjugations. 4 conjugations, with different forms active and passive, indicative and subjunctive, for present, imperfect, future, perfect, pluperfect, future perfect.
OK, that's a little extreme. I would start of by just learning the first three declensions, since they are the most common, and the following conjugations:
Active Indicative, present, imperfect, future, perfect, pluperfect, future perfect.
Once you have that down, you'll be able to read short and simple Latin stories and phrases, and a decent amount of the Common parts of the Mass. You should also be able to at least get the gist of the four Gospels in the Vulgate.
I would also try reading some Classical authors. Naso is the easiest, IMO.
For Latin books....I recommend Henle, just because that is what I'm most familiar with.
I doubt that an "immersion" program would be good for Latin, simply because grammar and syntax is a lot more complex than most modern languages. It is however more logical, so that's a plus.
The most important thing, after memorization, is to get a feel for the sentence structure; it is very different than English.
English: Subject-Verb-Object. For example: Rome is in Italy.
Latin: Subject-Objecct-Verb. E.G.: Roma in Italia est.
There is a lot more to this subject.....I may add more if time allows.