We are a year ahead of you, mostly walking 6-12 miles a day but we have no hills in SW Florida. We tried to make up for that by carrying a heavier pack but unless you start before sunrise it just gets too hot most days.
I have walked my way thru a pair of Altra Lone Peak 6s Mid Weatherproof so far training and recently tried a pair of Keen Ridge Flex Mid Waterproofs that gave me blisters in the house... and a pair of Merrell MOAB 2s also Mids and Waterproof that were similar but much more comfortable and better fitting but they got so hot they caused heat blisters after 2 hours of wear. I am going with a replacement pair of the Altras since they have caused no issues so far. Thanks to REI return policy each only cost $5.99 shipping to get a refund to try them out, money well spent if it saves us hassles later on the trail.
So far our biggest hurtle is the airline weight and size limits on our carry-ons. Our plan is to wear as much heavy clothing and rain coat stuffed with as much as we can to get us under 8kg and cinch everything down as small as possible to meet the size limits. I'm sure we will all look like comical charm bracelets walking on to our flights in Miami and the one we have in Frankfurt. Hopefully once one the planes we can shed the weight back into our packs before takeoff.
September- October planning adds a few more pounds of clothing layers but with less rain and moderate to cool temperatures should make for easier daily traveling. We plan on staying in Pensions, municipals, and small hotels mostly and going with shorter days as opposed to overdoing it and needing rest days. We aren't constrained by a schedule so 40-45 days should get us there. We are still bringing light sleeping bags for those days we do stay where there may not be blankets provided. We may also have days where we send our packs ahead as a way to take a break, thankfully these services are available for that purpose.
You have already found one of the best resources in this forum, we have already met a few friends here that were willing to share some of their tips and wisdom with us.
We are all excited as the weeks tick down towards our departure, we can't wait to get started.
Buen Camino and Good Luck.