yes, if you are planning on travelling around a bit in the area I think that will be your most hassle free way of doing it and can all be done online before you go.
maybe look at a multi entry tourist visa instead. The visa is valid for 6 months from issue and you can enter up to 60 days on it each time I'm those 6 months (and extend by 30, so technically you could get 9 months
Lazada is easy enough. Iirc Shoppee seemed to require the payment card be attached to a Thai address. Was a while back I tried it so can't remember the full specifics