Definately force carbonate. Search the internet for charts because it is based on number of volumes of co2 and temperature. You say beerline....I'm assuming you have a cobra faucet or tap at the end of that line?
After you sanitize the keg, blast it with CO2. CO2 is heavier than air so it will stay in the keg. That way when you transfer your beer in, you'll be transferring into a co2 environment and won't pick up any oxygen ( oxygen in fermented beer = bad ). After putting the lid on, hit it with 30 PSI to seal the keg. Turn off CO2 and purge the keg ( pulling up on relief valve ). Hit it again, purge, again, purge ( like 3 times ) to get any oxygen out of the keg.
To force carbonate, I set my pressure and leave it for 1-2 weeks to carbonate ( cold beer will carbonate at a lower psi than warm beer ). Some people turn up the pressure and shake the keg to quick carbonate...but not me.