Started plnts from seed, time to re-pot, but how big?? 1 plant per pot, or more in a bigger pot? First time planting basil. Any tips?

Basil doesn't need a big pot to grow. 1 plant per pot from 4" - 5" is ok. Bigger pot can be used for more plants ... They are easy to grow.

They can be planted anywhere.

You can plant basil as a single or multiple. Pots should be about one-third larger than the existing root mass. Too large a pot can lead to too much moisture accumulating around the roots. Basil is ideally suited to container growing in normal potting compost. Water regularly (from the base if possible) and feed twice a month with liquid plant food. Basil likes sun, so make sure it has a sunny, protected location. Basil is very cold sensitive. Basil will grow well indoors on a sunny windowsill, so if you want to keep it going, be sure to move it indoors when cooler weather approaches. The type of pot you select is not nearly as important as the drainage. Make sure that the pot you select is well drained. Place several clean pottery shards or small, clean rocks in the bottom to assure good drainage. Basil needs about one inch of water per week. If rain provides this, then you will not need to water additionally. Some terra cotta pots can wick some of the soil moisture away, so watch moisture levels. Moist, but not wet is the rule of thumb.

you must check the root zone once the plant becomes bigger so the roots will not choke themselves once the have completely gone around the pot

basically any size pot depending on how big a cluster you want to grow