A secondary vessel can be used if you like,but isn't all that necessary. Some like to clear the beer & dry hop,etc in a secondary. But it's best that the beer be at FG before racking it to anything.
I & many others just leave it in primary. Let the beer ferment down to a stable FG. Then give it another 3-7 days to clean up by products of fermentation,& settle out clear or slightly misty before packaging.
Yes,you could add a measure amount of sugar to each bottle. But that's not a very accurate way of priming,as some may get more sugar than others.
It's better to use a bottling bucket with a spigot to prime & bottle the beer. Boil 2C of water for a couple minutes in a small saucepan,& add a weighed amount of sugar to the boiled water off the heat. Stir it until the water goes clear again to be sure it's completely dissolved. Cover & let cool a bit.
Make sure bottling bucket is clean & sanitized,then place bottling bucket below the level of the fermenter. Use a tube from the fermenter to half way around the bottom of the bottling bucket either from the spigot on the fermenter,or from an autosiphon in the fermenter.
Start racking the beer into the bottling bucket,& when you get a couple inches of beer in it,slowly pour the priming solution into the surface of the swirling beer. The swirling action will help mix the priming solution into the beer. But you can give it a few gentle stirs with a sanitized spoon anyway to be sure it's mixed.
Now,put the filled bottling bucket on a higher surface,like where the fermenter was,to get a gravity flow going with a bottling wand atached to the spigot on the bottling bucket. The bottling wand has a pin valve on the end that stops flow of beer. Sanitize your bottles first,then insert the bottling wand into the bottle till it touches bottom. It'll fill the bottle till the level of beer comes to the top of the bottle's lip. Quickly pull up a couple inches on the bottling wand to close the pin valve & stop flow of beer. When you slowly pull the bottling wand out of the bottle,you'll get the perfect head space by way of
volume displacement. Then sanitize a crown cap & place on top of bottle. Repeat till complete. I hope this helps...