To become friends with a villager, just keep talking to them daily. When you get to a certain friendship level, you can start giving gifts- you can find guides online as to favorite gifts for villagers, otherwise exotic fruit is a great option.
And 10 villagers is the maximum. If you want more, someone will have to move out. You either need to wait for them to move out (you'll start one day and find someone with that thinking expression, talk to them and they'll say they're considering moving, and you can give them permission or not- they WILL NOT move without permission) OR, if you have a campsite villager, you can invite the campsite villager to move in, and then choose one of your villagers for them to replace. That villager will then IMMEDIATELY pack up all their things and move out, the next day the lot will be marked as "sold" for the villager from the campsite, and then the third day the campsite villager will move in!
