I moved from Ohio out here to Phoenix about 5 years ago and can answer several of your questions. I'm way out in the west valley so a few of your questions I'm unable to answer because I'm not sure about how things are out in Mesa.

1. we do train outside in the summer. Training starts super early in the morning either before the sun is up or at sunrise. Starting running with a camelbak since coming out here and eat lots of salt all of the time from May-Oct.

3. 6 hour rides are possible if you start early enough. You can either make stops at home to refill nutrition or carry cash and stop at gas stations. The other thing my wife an I do is to ride 3 or 4 outside and then finish the ride on the trainer.

4. I have a garage gym. It's hot, even with fans and insulating the garage ceiling and doors. Last year we moved our pain cave, bike room into an spare bedroom. with the ceiling fan and a fan in front of the trainer it isn't too bad. We keep our house at 79 degrees in the summer so I do sweat a lot. I've done 6 hour rides on the trainer like that while my wife rides outside.(Someone has to stay home with our daughter)

5. races are typically in spring and fall. Each has it's own positives and negatives. Race in the spring and you don't have to do high volume training in the heat. But if you need to train before work it's going to be dark and cold.. Not Minnesota cold but in the 30's and 40's.. Race in the fall and you have to train a lot in the heat but it's always light outside.

Biggest thing I had to learn moving out here is that in the heat of the summer you need to slow down. Don't expect to go fast. It takes a while to acclimate to the heat here. But it's better than 8 months of winter. Just be prepared to get up early from june-sept.

Welcome to the area. I am also in the West Valley so I cannot answer your swimming questions. Moved here 6 years ago from Illinois/Wisconsin areas. I have been training year round and echo the previous responder that in the summer, your training is early in the morning (be completed near 10:00AM). Our group rides through Lifetime/West Vally Cycle start at 5:00 or 5:30. I am not sure how many 6 hour rides you want to be doing in summer but 125 miles would be a killer in the heat. Most of the century rides are March/April and September October. I did setup my bike to carry 4 water bottles and freeze 1/2 and put cold water in them just before leaving (I have a large freezer and a fridge with 2 ice makers). There were a few days I had to stop at a gas station for ice/water. For open water swimming we use Lake Pleasant. The community I am in has 5 pools 2 are great 25yd lap pools and always have a lane for myself. The local YMCA here has a nice 50M pool and a masters group. You may want to check that option out in your area.
I bought a house with an extra bedroom and put in a wall bed. That room is used for indoor biking but I rarely have to use it. I can't imagine using the garage, mine is usually hotter than it is outside.
There are many races available, have you looked at Active as they will list most of them? A few come to mind like Iceman & Xterra in February Morristown, Ultraman Arizona in March (registration closed), Bartlett Lake, Cactus Man in May, and of course the have and full IM in October and November. There are lots of small sprints as well as just running or biking races.

1. A lot of folks do. Many of the tri and bike clubs still do their group rides...but man it is hot. But...that's why you have a Wahoo, right? Think of it in reverse from Minnesota: you don't train hard outside in the winter, so you wouldn't train hard outside in the summer here. In August it will be 90F at 4AM on some days.

2. In the east valley there are a lot of pools. In Mesa Skyline and Kino are your main lap pools all year, and then more pools are open in the Summer. In Tempe there is McClintock. Scottsdale has a lot of pools open during the year, I've swam at Cactus, Eldorado, and McDowell Mtn.

3. Bring lots of water, or go up to Flag for a weekend.

4. In a spare bedroom? Right now my bike is set up in my living room, but my pain cave is normally in my home office.

5. We have summer races here: Deuces Wild Endurance Festival in Show Low in June. Then Mountain Man short course weekend is in July. Mountain Man Long Course weekend is in August. Big focus on IMAZ around here of course.

6. We have a lot of races at Tempe Town Lake: Lifetime, CactusMan, IMAZ 70.3, IMAZ, Sun Devil Challenge. Then you have Bartlett Lake and Lake Pleasant triathlons (both are nut busters for Olys).

7. Lake Pleasant, Bartlett Lake, Saguaro Lake, and Canyon lake. Closest ones to Mesa are Saguaro and Canyon. Not sure of the OWS sitch at Roosevelt Lake.

---

Washed up footy player turned Triathlete.

I live in the East Valley on the Mesa/Gilbert border. Great place to live with a big and very active triathlon/cycling community!

1. yes training in the summer can be challenging but it's possible. We start our Saturday long ride no later than 4am (usually 3ish). However, in the dead of summer it's still over 90 degrees plus humidity during the Monsoons. As said above hydrate and slow down!

2. I am a member at LA Fitness. I like them because I drive around the valley for work and you're never more than 10-15 minutes away from one. There's 5 I can think of just in the Mesa area. As said above Skyline is also great.

3. See above. 3 am :)

4. Pain cave is in the garage in the Winter and my home office in the Summer.

5 and 6. Ditto for Deuces Wild in Show Low and Mountain Man in Flagstaff. Other than that we travel to cooler climates to race and make a vacation out of it. For instance, I've done IM Canada, IM Coeur d'Alene, you get the idea. Great races in the valley in the Spring and Fall.

7. We swim at Saguaro Lake. From where I'm at, it's a 20-25 minute drive. There is a group that swims there every Friday morning when it warms up.

Welcome to the valley! Tons of great riding, trail running, and tacos!