Hi there
I'm on week 5 (almost week 6) of the beginner rotation. Ill share my experiences...
Re: tubing & hand weights. I think this can be interpreted in a few ways: 1) mix and match like you said above. 2) do the 20 min, but only use the resistance described (ie: no weights during the weight section, only use the tubing during the tubing section, or vice versa) and 3) just do the 20 min w/ weights and tubing, as much as you can.
I just did the weights and tubing both, and did the whole 20 minutes. I did this for the first 2 weeks.
Week 3 I realized I did not like the lower body add on, so I subbed it w/ a low body premix from LIS Trisets. You can do a simple swap like this too, the rotation will still work. Some probably prefer to stick to rotations as closely as possible (meaning if they have the DVD, they don't sub even if they don't like it) but I asked and got the answer that yes, it's ok to sub if you want.
Let me know if you have any more questions about the beginner rotation! Good luck! BTW, are you on week 1?