Up-rating a chainring

Don't change both the chainring and freewheel at the same time, try a different chainring with your current freewheel. Then if you need to change your freewheel.

1.) Yes just buy a chainring with the right BCD and a chainring tool, and you should be able to do it yourself. (Assuming you have a crank puller to get the cranks off the bottom bracket in the first place.)

2.) Yes most probably you will have to lengthen your chain.

3.) I would say it will feel a little tougher at first, but you will get used to it.

don't listen, change sprocket first, then chainring if needed