Re: wearing tikkah
It depends entirely on what other jewellery you are wearing. Avoid wearing a necklace, earings and a tikka as you will look very OTT. Unless they are small and delicate. The tikka size should depend on the size of your forehead, the bigger the forehead, the bigger the tikka can be.
Your suit is very pretty, has lots of kaam on it so I would avoid wearing a necklace, earing and a tikka would do fine. For the mehndi you could have a middle parting and a plait, that would look cute. On the wedding, maybe a puff with the tikka in the middle.