Can someone please verify my calculation?

If a click is an mp wash don't you get 18 mp each click? MP wash gain = base int/10-2

 

200 base int gives you 18 mp each mp wash

 

yea divided by 10 and rounded down so if you mp wash with less than 10 base int you will lose 2 mp.

 

With 200 base int and no gear at all you will get 110 mp each lvl(from lvl up + 5 mp washes), if we were to ignore all the mp you'll be getting while getting to the 200 base int you'd need to mp wash for 47.7 lvls.

 

Each AP you throw on MP will give you base int/10 - 2 plus the 12 you'll lose when resetting that AP out to your main stat(or int if you're still adding points to it).

 

You are only considering half of the mp wash process when looking at it. Like others have said above, need to consider the point taken out of MP as well.
Yes, you will only get (base int /10) -2 MP per full Fresh MP wash

You also need to consider you will not have that HP immediately unless you're going to use stale HP washing. You'll still need to level in order to get the fresh AP to wash to 12k HP. As a BM, you'll get 18 HP per fresh wash, meaning if you find the 7000HP you need is correct, you need to wash 7000 / 18 = ~389 times (78 levels of AP). To do 389 washes, since you lose 12MP per wash, you need 389 * 12 = 4668 extra MP. To give you the exact amount you need to MP wash from level 70, you need to consider your goal level you want this HP by, your base MP at level 70, your int gear, and whether you will have mw (and what level it is) when leveling.

Note: I bolded extra MP as each class has a formula for the minimum MP they can have at a certain level. From Nise's formula compilation, it looks like this for BMs:
(lvl * 14) + 135

so if your goal level is 155, that means you can have a minimum of (155 * 14) + 135 = 2305 MP as a BM, so you would need 2305 + 4668 = 6973 base MP at lvl 155 to wash 7k HP