1) Depends on what you mean by viewing. If he's just opening up houses for you to assess as an investment, rehab, etc. then it shouldn't be a big deal for him to take calls. If you're in conversation with him or asking questions and he's inattentive and telling you to hold on, then find you someone else.
2) Not unreasonable but find someone else if it bothers you. My whole office has been AWOL for about 10 days now, even the broker, lol.
3) Depends on the nature of the call. If you're telling him you want to submit an offer on a property then by all means he should be very responsive. I wouldn't think twice about finding someone else. If he's shown you five houses and you just want to see more, then his actions are reasonable.
4) I went through real estate school last year, as an investor, and I can tell you ARV was never mentioned and was not on the test. Nor was any of the other lingo you'll pick up in flip books.
Why don't you get your license? That's what I did for many of the reasons aggravating you now. Most real estate agents are only interested in preapproved owner-occupied clients. They want to find a few houses meeting your criteria, show them to you, and close the deal. They don't have time for unproven investors wanting to view a home at a moment's notice just to submit a low ball offer which probably won't get accepted. With my license I have MLS access, the master key to look at most properties and I can write all the offers I want, when I want.
Until you prove yourself as an investor you need to take it easy on your agent because he/she will become disinterested very quickly. Also, instead of asking about ARV, ask the agent "After I buy and rehab this property, how much will you be able to sell it for?" If they know there are two transactions to profit off of they may be more willing to comp a property for you. They're not going to do this often so don't request it on every home. Besides, you should already have a good idea of ARV before you ever visit a property. Use the realtor comps to confirm your ARV just before you make the offer.