Can I put hot drinks in any bottle?

No. Only insulated stainless steel bottles explicitly rated for hot liquids. Plastic and single-wall aluminium bottles are cold-liquid only and can be damaged or become unsafe with hot contents.

How do I get the smell out of a water bottle?

Soak overnight with a tablespoon of bicarbonate of soda in warm water, scrub the lid seal separately, and dry with the lid off. Most odour lives in the silicone gasket, not the bottle.

Are time-marker bottles useful?

They work for people who forget to drink during the day, purely as a visual prompt. Individual hydration needs vary with body size, activity and climate.