sprockets and chain length

it would be preferred not to use more than 1 masterlink in a chain. depending on where the adjustment is you might not have to add and any links

It would depend on the condition of the existing chain. Measure it and see where it is according to pitch growth. If it is more than 1% longer than stock, then adding a new link of any sort could be a bad decision. It would mean that you are running two different pitches....which can cause premature damage and growth to your chain and sprockets. If it's a beater bike, go for it and be sure you connect the new master with the forks going the right way. A master weighs more than a regular link, so physics says it should probably be placed half the chain length away from the other. (not a big deal though)
Before you decide if a longer chain is needed, make sure your adjusters are all the way in.