You can follow the manuals and do your own upgrade. Or you can hire your VAR to do it for you. I know that when I worked for a private company I would do our own upgrades.
1. They were in a test environment,
2. They were a copy of the db's that we had in production.
3. I would spend close to 6 weeks doing the initial upgrades and making sure that I had all the additional keys, that any 3rd parties I had keys for and had the additional versions of the new software. As well as working out any issues that I found in the upgrade
4. Would verify that all my reports came over. Would setup some of my users in the test company for them to go in and verify that everything was working and set up a test plan. (including SSRS).
5. Would verify that nothing was feeding off of my Great Plains system being used in other db's. And if there was would need to test.
6. I would document everything while I was doing it so that when I went to the QC server I could follow the documentation and do everything again, following the documentation in order to get a feel for what the timing on the upgrade would be. (2 weeks). Then testing out to production users.
7. Would setup all my new servers with the software for the upgrade. As well as terminal servers with MR2012 latest version.
8. And finally, we would do the upgrade on Production.
9. Will have setup a training manual for all the new features for training while the upgrade was occurring or immediately after the upgrade.
10. So, if you have 8-10 weeks you can do your own production upgrade. Or you can hire a VAR who will do all the work and discovery for you and they will do a test upgrade, set everything up, know what the errors are. And can come in and do training for your users with the latest and greatest tools.
So all depends on whether you have someone on staff that is willing to take this on as a full time job for the next 8-10 weeks and how experienced they are with Great Plains. BTW, I have over 20 years experience and this is how long it takes. (8-10 weeks at about $4000 a week for a competent person) Guess it's up to you on which way you want to spend the money.