Changing the color of house trim is really easy and inexpensive. Normal preparation is to either pressure wash or simply wire brush and scrape any loose paint off. Use a good quality primer, tinted similar to your finish color, then apply the finish coat. No need to strip or remove old paint.
Your first step should be to go to a full service paint store to discuss the project. It is tempting to look for the best deal, but you will get what you pay for, and I think you will see a big difference if you avoid discount big-box stores for buying paint. Buy the best quality materials you can lay your hands on, then take your time, you have all summer.
I usually work on the side of the house without sun, so Western and south exposures in the morning and eastern and north in the afternoons. Stock up on quality ladders, brushes, drop cloths and whatever makes the job easier and more pleasant for you. If you have any slope on the lot, I have found leg extensions for ladders that accomodate uneven ground to be invaluable (about $45).
The quality of personnel in department and big boxes varies widely, but in general, you will not find the expertise and committment as you will find in the small franchise stores (Benjamin Moore, Sherwin Williams and independent paint stores) where the owner depends on consistently providing high quality materials and service to survive.