MashAllah. Congrats on the new ride. Drive safe. Good to see side mirrors not removed.
1.You can go for dunlop, dsi and Indian brands available in the market. Size 100/90-18. I have dsi tyre.
2.dont go for hid unless you can get a projector hid.
3.its ur choice here. If you don't feel the performance of spark plug up to the mark you may get it changed. I would recommend to use it till it give up its performance. Aise pese zaya Karo ge aap. When it's doing its job let it do.
4.I changed the stock muffler to a custom made muffler to get some 'dhaishat ' sound. It was just my shashka.
Use good quality engine oil and correct grade. Such as Liquimoly. Result is amazing.