Biko - the Travelodge at Preston Park is a popular choice (overlooks the start, although is a mile or so from the finish). Alternatively there are umpteen options along the seafront if you want to be closer to the finish and then it's a nice stretch of legs up to the start on the morning. A lot of places have a 2 night minimum stay so bear that in mind when booking. Also EVERYWHERE gets booked up really early, so if you want to book somewhere do it sooner, rather than later, otherwise you'll end up staying out of town and need to train it in on the morning.
I recently ran a 50 miler (SDW50) which was my priority, then 8 days later ran Brighton marathon. Inbetween the two I just did 2 x easy 3-4 mile runs, lots of dog walking to keep my legs moving, but also had lots of rest/sleep/good food, as well as a sports massage. My plan was just to see how it went for Brighton and if needs be treat it as a long training run for the TP100, but I ended up running a 5 minute marathon PB and it actually felt like the easiest road marathon I've ever run....so not quite sure how that worked! But the point I'm making is that it's easily doable, but just take it easy between the races as recovery is key.
More than enough time, the race starts at 9.15am and the park is only a few minutes walk from the station. One thing to bear in mind though is that you have to pick your race number (or get someone else to pick it up in your behalf) on the Friday or Saturday.
The only bit of the course I find congested (and which I don't like) is the first mile around Preston Park as it's quite narrow in places and you get people starting in too fast a start pen and holding other people up....but it quickly opens up and then I don't fnd any problems with congestion.