Will not be using Aluminium for sure. Now about the size of the wire for the primary. What is the difference with the gauge of 22 and 16. isn't 16 more space taking as that is more thicker ? Moreover i will be filling the remaining window with the secondary with 2 or 3 Gauge flexible copper wire whichever is available here. probably 3 or 4 turns if possible to get the max current out of it.
Question is if am drawing that much current at the secondary would that heat up the primary with a thin wire like 22 AWG wire ? or would the sweet spot be 16AWG ?
Yes #16 will take up more room than #22, but if that was the only consideration then why not use #34 wire as that takes up less room than #22.
The whole thing is based on how much room the primary takes plus the secondary, and because there is a relationship between the primary turns and secondary turns for both voltage and current, this creates a situation for optimization of primary and secondary wire sizes. Once you pick the primary wire size you know the secondary wire size because you know the primary voltage, secondary voltage, turns ratio, and thus you know the secondary current.
For example, if you use a wire size for the primary that has cross sectional area 1 unit and the current is 1 amp and voltage 10 volts, then if the turns ratio is such that the secondary is 1 volt then the second current is 10 amps. This means you know the wire size for the secondary as it must have a cross sectional area of 10 times that of the primary, which would then be 10 units.
What this means is that we know the primary size and secondary wire size, and we then proceed to see how it fits on the core in the window area. If it fits perfectly then we've optimized the design for the given input voltage. That gives us the maximum current output on the secondary. If it is too large we have no choice but to lower the primary wire size which then makes the secondary wire size smaller too. If it is too small then we know we might be able to increase the primary wire size (and thus the secondary wire size also) but there is a catch and that is if we get too close to the max going up even one wire size may go over the limit of the window area so we have to back up and call the first try the optimum.
So to recap, once you choose the primary wire you know the secondary wire size, and then you can try to figure out if it all fits in the window, and this will result in three possible cases:
1. It fits perfectly.
2. It goes over the window area limit.
3. It does not use up the whole window area.
Depending on the case you may or may not try to increase or decrease the primary (and thus secondary) wire size.
Because of skin depth you also dont want to use too big of a secondary wire size. 1/4 inch diameter is probably a good limit. If you need heavier wire, use two turns wound bifilar.