I am going to start with describing my plant and how it has grown and its living conditions, and then I'll ask my questions later. So I have this indoor avocado plant which I planted from a nut and it is dearly loved by me. I named it Bertil. It is about eight months old, about 40 cm/16 inches tall from the soil up, and due to arctic climate I cannot plant it outside. I just moved a little more south so it won't be affected by the eight months of darkness, though it will get a little darker during winter. Also our house is a bit cold, around 18 °C (depends whether or not it's sunny outside). I don't know what soil I used, my mum just recommended it. And I don't think there is a lot of salt in our tap water as the main source is surface water from lakes etc., but I could be wrong. I water it daily, but not too much. I keep the soil moist. Some say I should let it dry out and/or soak it once a week. I am confused.
Some history of Bertil. I repotted it during summer, late June (it's now late October) and it had a huge growth spurt since then. I originally had two plants, where one had two stems from the beginning, but died of unknown reasons. The one that survived originally had just one stem, but after repotting and a car drive it suddenly had a new, long stem, which in the end is the one that grew to be 40 cm. The original stem hasn't grown more than 2-3 cm.
I try to keep my plant in the sun and at not too low temperature. I don't over water it (I think). I have been reading here for tips, and I noticed it was recommended not to water in the saucer or have gravel/rocks in the bottom, and I have/do both. It has gotten pretty big now (as mentioned), but there are a few things that worry me. The bottom leaves especially and some of the above have started to curl a little at the tip and I know they should be smooth. Also the lower leaves have gotten brown tips. It's rather healthy otherwise and there is new leaves at the top. Some time ago I plucked it at the top to encourage the lower leaves to be bigger, and it has helped. The top leaves are huge! But I am worried. Especially now that winter is approaching. How much sunlight does it need, what is the ideal temperature? Should I water it differently, or how should I water it? It's doing ok now, but some of the leaves have started to curl and turn brown at the tip; is this a warning sign?
So the questions are:
Should I do something as winter is coming along and it will be colder and darker?
Why are the leaves curling and what can I do to prevent it?
Is my plant dying?
Should I perhaps repot it and how?
Am I watering it wrong?
I would truly appreciate if someone would take the time to reply because I would be very sad if this plant died. Also it is a wonder something hasn't gone wrong earlier as I probably potted them too early in the ceramic pots.
Here are some pictures of it now: