Hi,
My first RIAT was in 1991, so I hope the following helps.
RIAT is incredibly busy, and the first challenge you are going to have is getting there early enough. Assuming you live in Ipswich, unless you are planning to leave at a ridiculous time, you are going to need to stay locally - you will want to be getting near to the base by 6:30 at the latest, which will allow you to join the queues for the car parks.
Once you have parked, you will be faced with another queue (albeit this time on foot) to actually get into the airshow. The gates don't open until 7:30, but join the queue as soon as you can, because by 7:30 it will be long.....
To get in, you have to go through an airport style security check.
Once in, you have to decide what to do. If you are planning to attend both days, you may choose to spend one shooting the static display, and the other the flying display. One of the advantages of getting in early is that the static area is relatively uncrowded, which makes it a lot easier to get shots, especially of the larger aircraft or if you are going for a more arty type of photo.
Getting in early also means that if you plan to spend the day watching the flying display, you can go straight down to the runway to bag a good spot. The best place to view the display is halfway down the runway - however, this area is full of corporate chalets and various public viewing facilities that you can use for a further payment. However, there should be plenty of space to either side of this area, albeit you may have people in front of you. Another popular area is at the end of the runway where they are taking off and landing from. If you are at the other end, aircraft taking off will be high by the time they have got to you (or may have turned away from the runway) and landing aircraft may not come all the way down the runway.
Don't leave when the flying display ends unless you want to again get stuck in heavy traffic. You should leave either just before the end of the flying display or alternatively, go for a walk around the static display after the show. Again as the showground empties, you can get uncluttered shots and some wonderful light as the sun starts to set.
Instead of going to both show days, it may be worth going to one of the show days and then either the arrivals and departures day. Not only will this be cheaper, but you will also avoid a second day of traffic congestion and crowds.
The departures day on the Monday offers an excellent opportunity to get a record shot of the air show participants, with most just doing a routine take off. I usually arrive at about 8:30-9:00 and am never on the front row, but usually get a good view. Expect to be on your way home by about 2pm, as by then almost everything will have left.
On Friday, as well as arrivals, you will also have the display aircraft doing rehersals and display validations, so this makes the day more like an airshow, with action right through the day.
You could do worse than go to the Friday Park and View and then attend the show on the Saturday rather than going both days, which could be a bit much (albeit there are many who go for the whole week).
My lens goes upto 300mm so you shouldn't have any problem with the converter.
Hope this helps.
Neil