Taking CaCO3: 144 to mean that the alkalinity of the water is 144 ppm as CaCO3, assuming that its pH is 7, you are mashing at 1.4 quarts/lb of grain and that the grain bill consists of 85% base malt with DI mash pH of 5.62 and buffering of -41 (at 5.62) and 15% caramel malt with DI mash pH of 4.66 and buffering -48 I estimate mash pH of 5.64 w/o any acid addition. The fact that this is close to what you got with EZ (5.67) does not imply that either of them is correct. These estimates have to be taken with a grain of salt. Under the assumptions I made, 2.5 mL of 88% lactic acid will take you to pH 5.52. Three mL would get you to 5.49. Now while I am certain my mathematical models are more robust than those in the other calculators I am not certain that my malt data is any better than theirs so you have to take my estimate with as much of a grain of salt as you do anyone else's. Also, I had to make several assumptions about your grist to water ratio, whether the CaCO3 number is really the alkalinity and that your water pH was 7.
I have no idea what your CaCO3 or RA should be either which is another way of saying it doesn't matter as long as you account for the presence of alkalinity and calcium hardness in the source water.
Assuming the CaCO3 of 144 does mean that the alkalinity is 144 cutting it 1:1 with RO will reduce that to 72 so you probably don't need to acidify the sparge water but as it is so simple to do and as you have been plagued with astringency you probably should for insurance. 72/50 = 1.44 mEq/L and you will need about 0.7 times that (0.9 mEq/L) acid. Ten percent phosphoric acid is approximately normal so 0.9 mL per liter of sparge water treated should do.
All salts and acids here should be added to the mash water as you are relying on the calcium to lower mash pH by 0.1 unit. If you had enough dark malt or wanted to use more acid and then wanted further pH reduction in the kettle you would add salts/acids there.