What type of equipment are you using? Are you able to heat the mash tun or are you adding hot water to raise the temp? There are calculators out there that will show you how much water at x temp is needed to raise the temp of x amount of water.
Have you had a problem with chlorine taste in the past? If you have highly chlorinated water that has caused problems in the past, i can't imagine why adding to the mash vs strike water would be a problem since chloramine wont boil off regardkess. Unless there is a pH issue regarding metabisulfite?
This is an important point. Munich is made a bit differently than crystal malts so it will have a different profile, relying on color only is going to become a problem is the finished beer.
Was the mash sample well homogenized? Could be sampling error. what kind of beer is it? A kolsch post boil pH will be much different than a double IPA post boil pH for example.
You can really use any acid. Lactic acid may be more commonly used than Ascorbic. We would need your grain bill and water profile to really get the amount dialed in. Without a pH meter, it's going to be tough to see if the amount is correct. The calculations are based on current pH, grain amount...
Standing water is usually pretty gross. Once fermentation begins, the positive pressure in the fermentation vessel is going to keep creepy crawlies out of there. I'd say it is probably not an ideal location but probably of much concern either.
If you aren't too concerned about the flocculation i don't see why this wouldn't be ok. Its recommended for a cream ale so its going to be a pretty neutral yeast profile.
Bubbles are not an indication of fermentation activity so its good that you are checking gravity and using that information. 1056 and 001 can both be fast, 68 would be right in their comfort zone. Sound like that starter did its job, should be a good beer.