To reinforce some of the points – there is absolutely no dress code on the grandstands, dress for the weather. I’ve never heard of anyone being turned away from the bars around the port area after the race because they weren’t dressed up but if you were to attend on of the Michelin star restaurants for example, some of the hotel bars or the Casino you may have to dress up accordingly.
Definitely take sunscreen, a hat, sunglasses, a rain poncho just in case, ear defenders…and a seat cushion! Also look into renting a FanVision unit (or one each), they have had some signal problems in the past couple of years but when they work they are great little miniature TVs which allow you to follow the race stats, your favourite driver, commentary, etc.
T high is a good stand, 4 days is a long time in one spot in Monaco but I’m sure you will have a blast. You could always if you wanted to mix it up a little and do something else on the Thursday and/or Friday (e.g. view from a yacht or a yacht party at night) which would be relatively inexpensive by comparison to the weekend…but you’ve already paid for your tickets for those days so you would be paying twice!!
I hope that helps, if you have any other questions don’t hesitate to ask.