For the potty issue Personally, I would do away with the potty pad and just outdoor train him but the same method can be used for both areas really. Monitor him closely all the time, use baby gates or tether him to you if need be and when you catch him going inside/ off his pad say "ah-ah no" scoop him up immediately and move him to the correct place. When he goes in the correct place, praise him like crazy, give a treat too if you choose.
As for the separation, giving something like a kong filled with peanut butter or non-fat, sugar free, flavorless yogurt (found in the organic section of most grocery stores, very inexpensive) freeze the kong and give that to him when you go to leave so he gets a special treat that makes it more enjoyable. Also, there's a book called I'll be home soon that is very good at helping you deal with SA, lots of good info on desensitizing and tips/tricks to help your dog.
I wouldn't get a second dog unless you're commuted to a second dog and I'd caution that a new dog might come with it's own issues and could pick up on puppies bad habits or teach it more bad habits. Twice the dogs is often twice the work or sometimes 3 times more haha. Good luck.