Wa Alaikum Salam Bro.
1. For Brake Fluid, I would recommend to go for liqui moly instead. yes liquimolly is good
I think, you should go for DOT 4 instead of 3.
2. Bro, if transmission oil has never been replaced in these 70,000 kms, it is very strongly recommended to change it now! Normal span is 40,000 kms, it has already covered 75% more than its limit. i dont have service history of the car. So i think i must change this fluid.
3. Use OEM recommended plugs. Do not change its specs. please suggest which one are the best
4. If you will be using 5w30 and from liqui moly, then stick to liqui moly and 5w30. Buy genuine engine oil. Do not switch between different brands and grades of oil. 5w30 is fixed as per user manual. Genuine oil i will check with toyota 3s
5. You can get your vehicle tuned from any good garage / workshop. I would not recommend Toyota dealerships. my friend as i said just tuned his car from toyota and tney charged rs1800/- They are extremely expensive. Well, if you can afford, then you may surely go there.