Boiling doesn't ruin the polyfill, but there are better ways to clean a carto than by boiling. Check you tube. You can make a carto plunger thing with a condom and a syringe. See youtube vid by kennysmancave.
Burning the polyfill is from not keeping it wet enough. You need to top your carto off regularly as you use it. A drip tip is good for that because you won't need to pry that rubber cap off the carto each time.
If you want to try a lot of flavors, yes, keep cartomizers for the flavors you like and use attys for teting.
Atomizers are unpredictable. Sometimes they last a day or two, sometimes a month or two. Clean them regularly and a good atty will last at least a month or more. If you only use it to test juice, it should last much longer. Make sure it's wet enough but don't flood them.
Sorry, I forgot that a 510 drip tip fits an 808 carto.