what if we are capable to handle our affairs but want to establish a relationship for guardians/conservators before they are needed?

If you have a valid Medical Power of Attorney and a valid Durable Power of Attorney, you may never need a guardian.  But, just in case, many states allow you a sign a Declaration of Guardian in Case of Need naming who you want and, in some states, who you do not want.  Check with a local elder lawyer.  You can use the Find a Lawyer function on the website of the National Academy of Elder Law Attorneys (www.naela.org)