Dillon makes pretty good equipment for certain. I have a few of their loaders. Just sold my 550. As far as conversions I happen to have a couple full conversions with the powder measures etc but you really don't need them. One thing that is nice is a couple of the knobs that you can buy on ebay etc so you can adjust the powder measure without a wrench. Dillon does not sell it though. Another nice item is the Strong mount for the 550. I have these on all my dillon reloaders as well as a Redding press mounted on one. I put the whole thing on a piece of plytwood or OSB and attach the whole thing to my bench. I also do the same with my Spolar and PW shotshell reloaders. That way I can take one off the bench and put another loader on in the space of a few minutes. I even have 4 Mec Sizemaster single stage shotshell presses done the same way for load development. There are lots of neat things you can buy...but wait till ya think you REALLY need those items. I also have a Dillon electronic scale that gives me quick weights...but i still use a RCBS 304 scale for most of my weighing. I trust the old style scales much more than these newfangled electric thingies
Most of all take your time..keep weighing the charges till you are satisfied it is dropping the amount of powder you want(You'll probably be as paranoid about that as i was.)....and have fun!! and be careful. You probably WILL shoot more!