Re: 7 months old, how many wet diapers.
according to LLL, "Once mother's milk comes in, usually on the third or fourth day, the baby should begin to have 6-8 wet cloth diapers (5-6 wet disposable diapers) per day. (An easy way to feel the weight of a wet disposable diaper is to pour 2-4 tablespoons of water in a dry diaper.)" i would think this would also apply to older babies as well.
also...as long your 7 month old is gaining well, you know that he/she is getting enough milk.
per LLL, "The baby should gain at least 4-7 ounces per week after the fourth day of life."
kellymom's site states that average weight gain for 6-12 month-old babies is 2-4oz a week.
....so with that said, if your baby is gaining about 4oz or so a week, he's/she's doing just fine! 
HTH!
Mommy to...
Aleina... born on Mother's Day, May 14, 2006...7lbs 4oz, 21.6 inches
Lauryn Elle...January 26, 2008...7lbs 15oz, 20 inches