Thanks for the advice and the woodblock skimmer tip @ROB . I'll check out the youtube vid you linked, personally I've been following Inappropriate Reefer's $146 build.
My plan to keep the temp stable is to get a AL60 TEC chiller. Don't have space for a full fledged Hailea and I'm pretty sure that will be overkill for 10 gallons lol . I'm using a XD20 (rated for 20l) for my 19l FW tank and it can keep the water stable at 26-27c easily, max temp delta i achieved was -4c below ambient. Since the AL60 is rated for 60l i think it should be fine on the 10g/40l tank.
About weekly water changes, I'm aware you can rely on that for nutrient export on nano tanks but I'd prefer to buy some leeway with a skimmer and hob refugium in case life gets too busy. Hard to predict with a 2.5 y.o. kid sometimes. Seems like 3 sides of the tank might end up with some sort of HOB equipment hahaha. Let's see how it goes.
Anyway, today I was thinking hard about which 2nd hand light to get, AI Prime / Kessil A80 / Spectra Aqua Knight. Each one is almost double the price, the price difference can buy a lot of other stuff. Personally I really like the Kessil shimmer, but the value of the Aqua Knight is hard to beat. 30W and the light quality seems decent and a lot of positive reviews.
@equiox - Trying to keep it under 1k, so far I've spent $80 for salt, rock, bacteria and refractometer.