Your Ck-30 is 2½ ton. The 5 year old coil may well be 10 SEER. Even if it is 13, you can't get away with oversizing the outdoor unit. If the coil is 2½ ton, that is a problem. But it also is quite possible the coil is rated 2½/3. Your service tech should be able to determine if there is a proper ARI match on your new 3 ton unit to the existing coil.
Do you have the equipment to bleed nitrogen while your are silverbrazing the new pipe connections? Very few contractors I know would touch the arrangement you are proposing. Would they be willing to put THEIR warranty on this system???
Are you going to use a Dry 22 unit? or switch to 410??