If you buy tri-bars, make sure you practice on them. Strange feeling first of all, steering with your elbows. Also you need to get used to trying hard in that position. Before riding a 12hr I used to do 100m rides on the tri-bars, just to get used to the position.
Training wise 3 sessions which may help:
1. Long rides of around 2 - 3 hours, preferably with some hills and stay in the saddle pushing a largish gear up the climbs to build strength.
2. Find a club and do some evening 10m TTs. Getting good at time trialling requires practice. Even better would be to ride as a 2-up so you can learn from someone else.
3. Find a flat, straight, quiet stretch of road measuring 1/2 mile. Twice per week ride 6 - 8 flat out 1/2m intervals (should take just over 1 min) then turn around and ride slowly back to the start. You will need a run up so you hit the start of each interval at required speed. Do this for 2 months before your target race.