[tlg]

I should have this in stock within one week, later I will begin training. Any advice?

It would help to know what are you training for?

 

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Right now, I can easily go, but when I need to stop, it is a bit hard for me. Will need to practice.

Make sure your pedal retention is set to the easiest level. You don't want them too tight to start.
Does your husband have a bike trainer? If so, put your bike on it and just practice clipping in, pedal a few times, and clip out. Keep doing until you feel comfortable.
Or practice stopping/starting on a grassy area or a bicycle path. It won't hurt if you fall over and you'll be safe from getting run over by a car.

Also, I feel it personally how we really need the bike shorts

YES!

 

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That's a sexy bike, but you're taking your pictures backwards. Always take the picture with the drivetrain facing the camera.
It's the law... don't break the law.

Like this!

 

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First time group ride last Wednesday night, they are really really fast, average speed over 30km/h, I am at. 23km/h, though I am the last one in the group, but my average speed also increased, used to be around 18-20km/h. Hopefully more group riding and I can finally catch up someday

Awesome. Congrats... you're really addicted now

You are probably strong enough to keep up with them right now. But being new to group riding, it will take you some time to learn to ride safely at close distances to other riders. Once you can do that, you can benefit greatly from drafting other riders and will keep up no problem.
Study the other riders. Learn who are the most consistent riders. The ones who don't do dumb stuff. The ones who ride a nice steady pace in straight lines. The ones who communicate well. Those are the ones you want to learn to ride close to.

 

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So I finally finished my first 100km ride, and get a 120km ride at last, last Sunday. All happened unexpected

Congrats! Some of the best rides are the ones that happen unexpectedly.