I would like to train for a community race(20 to 100 Kms) called "Ride don't hide" with my cousin who has agreed to form a team with me. I don't know yet how she plans to train but I have been looking at road bikes, I am going to follow a Cycling Weekly 3 month program. I have been volunteering for other mental health fundraisers as well but had really wanted to get physically involved. Yesterday I spoke with a sales person about some bikes that may suit me. He doesn't work on commission so he doesn't have any reason to sell me any one kind. The bikes he recommended were the (according to him the best bike for me)Trek Domane ALR 3, ($1500), and some other options Trek Domane 4 ($2000), Cannondale Synapse ($2000) and the CAAD 12 ($2500). Obviously, I would like to train for other races, not just this one. I really just need some help deciding what is the best ride for me as I really don't understand what is best. Some of the challenges that I am working with are that I have a bad back and early onset osteoporosis.
Presently I have a commuter hybrid mountain bike, big frame, and thin tires. I dusted it off just yesterday and rode over to the local bike shop. I would like to buy locally as it easier to commute(as I don't have a car) there for repairs, although the store is a franchise and the bike can be serviced anywhere their stores are while under warranty. Maybe you can all weigh in and give me your two cents. Greatly appreciated.

Buy the bike that fits you best from the shop that treats you best.

This, and give them an idea of what your budget is.

Those are all very nice bikes. The Domane and Synapse are endurance bikes and will have a more relaxed geometry and may be more comfortable. The CAAD 12 is also a great bike but it has more traditional geometry with a horizontal top tube. I recommend you test ride lots of bikes to compare.

One piece of advice..... tire pressure can make a big difference in how a bike feels. I test rode a bike that had over inflated tires and I could feel every little bump in the crappy road. Wider tires with lower pressure will give a smoother ride. Make sure the tires are inflated properly on bikes you test ride.

I'd find a new shop, if they are quoting you $350 over MSRP for the Domane ALR 3 https://www.trekbikes.com/us/en_US/b.../1402000-2017/

It will work out a lot better for the charity if you just donate the two grand!

Visit lots of bike shops until you find a shop (and owner/employees) that you feel comfortable with. Then test ride all the bikes the owner suggests and buy the one that "speaks" to you.

I rode my first few charity rides on a $300 used Trek. It was a horrible bike, but it was good enough to ride the MS 150.