You will need the 90cm one, which will cost you pretty much 2/3 of your budget alone. There is no point starting a reef tank with a budget in mind in my opinion. General concensus is it will cost around $2500 for every 100ltrs of water, this isn't even buying top range equipment.
The silicone will probably be pink as its been stained by some sort of chemical treatment in the past. Regarding the bracing, it really depends on the dimensions and thickness of the glass. If I were you I would just buy new glass or get a new tank made from someone locally, it's pretty cheap and will look a lot better than using an old tank.