Ill break it down:
Generally it is in good sense to apply broadly and apply early. The lower your stats are away from the averages (3.6 GPA 30MCAT), the more schools you would want to apply to until you hit a certain cutoff (generally, for most, anything under a 3.0 and a 28 MCAT is considered on these boards as grounds for pursuing a postbac (SMP), or retaking the MCAT, respectively). The higher your stats, the less schools you will generally need apply to. When you have unbalanced stats- that is a really high MCAT and a low GPA (and vice versa), you generally do not need to apply to as many schools as someone with low MCATs and a low GPA, but should apply to more schools than say, the average 3.6, 30 MCAT student. Generally, like when applying to college, students will have a few "safety" schools (the word safety is pretty relative as no med school is a safety- but for the sake of argument, lets talk about schools that you determine yourself that you will have a good shot of getting into. Remember, "lower tier" schools may automatically reject you on the grounds that they can safely assume that they are your safety school so choose your safety schools wisely. State schools (except cali) generally are safety schools for many students, but may vary from student to student and state to state. Students' undergrad institutions that have an affiliated medical school may also be a safety school (disclaimer: this varies from place to place and is not absolute). Followed by a pick of safety schools (generally around 20% of the schools they apply to for the average student), is a list of competitive schools- schools whose (putting into consideration private and public schools) averages match up pretty similarly to your own. This tends to make up the bulk of the list of schools that the student applies do, somewhere between 60-70%). Lastly, there are the reach schools, which make up the rest.
Generally most students apply somewhere between 10-15 schools. This varies with your stats and your confidence in getting into medical school. Now with that in mind
1) This varies from state to state. If you are a California resident, it would be prudent to apply to many more schools, as California schools are indeed some of the hardest medical schools to get into in the country. If say, you live in Ohio or Texas, you may get by by only applying to in-state schools, but the rule of thumb is, you will probably find optimal success applying to your instate schools as well as out of state schools (generally private since most dont have a state bias).
2) Top 10s are generally the reach schools I mentioned above. There are a few students who are studs when it comes to their stats and application. These students are the ones who will most likely be accepted to at least one top 10 school. For the average student, its good to have one or two reach schools (just be realistic if your numbers are way under average) just because the application process is a bit random sometimes, you never know. If accepted, you have to weigh in different factors including, but not limited to, 1) cost 2) location 3) the education & "prestige factor". Let's be realistic. The prestige factor plays a big role in decisions to attend one place over another. Though the education is the same everywhere you go, and generally where you attend shouldnt play a huge role in the match, the name recognition of a top ten school is always an attractive one for anyone. Keep in mind, these are not absolute things, but generally echo the sentiments of many students.
3) Again this is variable- the MSAR should be able to tell you the differences. The rule of thumb is that the In state public (of course not applicable to California) should be easier to get into, but this is by far not absolute and cannot be applied broadly.