Cheapest areas to park in town are around digbeth area where you can normally park all day for £2:50 ish if you go a few roads down most of the streets aren't parking meters down there so you can even park for free.
Only down side is that it's about a 15 minute walk from the start.
You should be ok getting to the Jewelery Quarter, since that side of town isn't affected by the closures. I'd guess the best bit is to get off the M5 at West Bromwich and come into Birmingham down the Soho Road. Then you can turn straight into the Jewelery Quarter off the ring road without hitting any of the closed areas.
Only thing to allow is a bit of time since that road can get busy if there's lots of traffic.
Looks fairly solid to me.. You only have a problem with going out too fast when you can't speed up for the last 400m, but those are fairly nice even splits, first and last will always be a bit quicker.
You'll get more improvement by targeting your endurance, which will enable you to hold faster times for longer. Keep up the tempo runs and increase the mileage of your longer run and you'll start to see it come down.