Pardon me for being very direct, but "Huh?". Sorry, if you don't have even a clue about how you are going to shoot it, what's the point? Nobody can answer your questions. We don't know your locations nor anything about your planned camera setup and other factors. Therefore it's impossible to even make a guess about required steps for post production, how long they would take and ultimately what they cost. Such stuff can involve tons of rotoscoping work, different methods of tracking in 2D and 3D and a lot of other things. Likewise, there is little to no point in asking for specific tutorials. I'm reasonably sure there is no "How do I put a boat in my scene?" one, but on the other hand, based on my hints I'm sure you can find oodles of ones covering the individual techniques just like you can find VFX companies that would be willing to do it for a good chunk of money.
4 scenes on location - I'm guessing 1 day, but it could be 2 or 10, depending on how many setups are in a scene. If you mean shots then it is probably just 1 day on location.
Compositing 4 scenes -- let's see, the average scene I worked on in the last project that we did was about 5 pages of script with about 7 shots per page or about 35 shots averaging 7 or 8 seconds per shot. But then again you could be talking about 4 shots so let's say that's a total of about 40 seconds.
Quick estimate: On Set visual effects supervisor - base rate $2500/day so $2500 to $25,000 for VFX Supervision on set
Compositing, averaging about 2 hours for each 10 seconds so that's $1200 to $10,500, Please note that without good preproduction planning and professional cinematography 2 hours could easily stretch to 8 or 10 or more.
Pre-Production planning for the 1 to 10 days of shooting $1,000 to $4,000...
So your price range from a professional would be somewhere between $3,500 to $40,000 depending on what you are planning. Give me a script, resume's of the production team, storyboards, scouting reports, and the rest of the stuff any reasonable person planning a production would supply and I can nail down the bid a little better. If someone in the US is going to make a living doing visual effects and pay their taxes and run their operation like a business I don't see how they can possibly operate on less than $150/hr. Double that for on location work because you need production insurance. You'll get an idea of how to estimate the true cost of production.