You have a bike you've been riding for 10 years. If you are sure it fits correctly and it meets your current and needs for gearing, brakes, wheel strength, etc. then you have a template. If there are shortcomings then concentrate on how to overcome them - lower gear range, hydraulic brakes, sturdier wheels. etc. As for fit, frame size is sufficient if you get a similar style frame. It's best, though to look at exact frame specs to make sure what you get can be adjusted for proper fit. As I suggested in the thread you referenced (though the OP ignored the advice) look up info on bike fit and frame geometry. In my opinion there is nothing that will have more impact on your efficiency and comfort than correct position and proper support, which means seat, bars, stem, cranks, pedals and shoes. No matter what the equipment or frame those items can make or break your experience.

Of course you can order a bike online. I mail ordered my bike from REI. I figured out what frame was close to what I already had and ordered that, knowing that I wanted wider bars with a different curve, a shorter stem, different saddle and clip-on pedals. I did not order a stem, though until I played with an adjustable stem to determine the best position. However, my calculated estimate of what I would need was on the money. But as noted above, not all bikes come with wheels (or other items) that are the best, so educate yourself before proceeding.