Repairing (repointing) stone retaining walls

Some stones had fallen off some stone walls in our backyard, and I decided to repair them - basically cleaning up the area where the stones should go, mortaring them back in place.  Note these are nominally retaining walls but the work I did was not structural - there is not a bulge or tilt to these walls, the stones for the most part were on the top or edge of the wall.

Materials

•  mortar mix, type N (Quikrete)
• used about 32 lbs. (2/5) of an 80 lb. bag
• Concrete acrylic fortifier from Quikrete
• used about 2/5 of 1 quart

Tools

• 10 gallon bucket
• small garden trowel
• masonry trowel
• gloves**
• (I didn't actually have these but I should have)
• small metal chisel
• handheld sledgehammer / pick
• wire brush
• garden hose with nozzle with jet setting

There wasn't much loose mortar to remove, and I mistakenly thought I should remove any/all old mortar - this led to me hitting the stone wall with too much force, and knocking of other stones and even an entire large section that was probably fine.  This just made more work for me to do, luckily it didn't appear to affect the structural integrity (it was at the end of a tapered section of wall so very little force / pressure / earth behind it).

I started by using a chisel and hand-held sledge hammer to try to remove the mortar, then I just used the wedge end of the sledge hammer - and that's when I used to much force.

I cleaned the areas and the stones using a small wire brush, and then sprayed it with a water from garden hose with the adjustable nozzle set to jet.

The mortar I used is from quikrete - it called for 4.7 L of water to mixed with the entire 80 lb. bag.  My plan was to mix 1 L of water, some binding agent, and 1/5 the bag of mortar.  What actually happened was  I measured 1 L of water into a 10 gal bucket, added some concrete binder (~1/10th quart), then added and mixed mortar powder until the consistency was thick and at least 0.5 inch of mortar would stay on the trowel held vertically (instructions from mortar bag).  I ended up making three batches of mortar to get everything done - I wasn't confident I could work fast enough to make more.

I applied the mortar initially with a trowel, but then just using my hands.  WARNING:  big mistake to not use gloves, the mortar is caustic!  My hands hurt for days, and the fingerprint swipe on my phone stopped working (mostly) because the skin had been dissolved off my finger tips.  

Here are some pictures of the results: