simple answer to first question: yes, you and your spouse can live outside one county (either or both) and then file the divorce in that county.  many lawyers do it all the time.  however, this is the general rule on venue regarding 26.09 actions under our RCWs...but...

..yes there can be repercussions, and every once in a blue moon i see those repercussions.  first of all you may not draft the orders in such a way that the final terms can be enforceable later in both other states or enforceable in washington as to the VENUE in other counties.  the circumstances surrounding venue issues can be subtle. if you are considering possible ISSUES that could come up ...ie such that your "deal" with your spouse may not be enforceable, or that you may end up having to file your motions in Lincoln county when and if things go south later on, ...either during the 90 wait period ... or later after entrance of final orders...if that is already on your radar then i would reccomend either myself filing and drafting your agreed divorce documents or another attorney or be on the totally safe side (but not always very cost effective) of just hiring a local lawyer in your county to do a court hearing with you locally (expect $1000 to $1500 retainers even for uncontested agreed cases) ... I file uncontested and agreed divorces using an online software system i programmed myself (i knew my 12 year old video game programming in BASIC on my ti-99 would come in useful one day... ie 26 years later...;)).....and it is only filing correctly and drafting the docs right that i can both avoid the court hearings that are part of the reason the local attorneys slap you with larger retainers... they also dont have auto document processing online... anyways... i can file for you regardless of even if BOTH spouses live outside of lincoln county) .... i don't advise you do the docs alone and  file in lincoln without a lawyer  if you have either money/debt/realestate or custody/childsupport issues at stake. ... even if there is nothing to divide at all doing it yourself is a nightmare if you have never done it and it may cause you to have to actually go there to correct or amend your filing... best of luck.....