The short answer is that most (all?) TrainerRoad training plans follow a 12 week base, 8 week build and 8 week speciality phases, so you've got plenty of time! I'd also recommend reading around a bit to get a better idea of the underlying reasons and arguments for and against this type of higher-intensity, shorter effort type training.
The longer answer - shifting weight. Getting down to your "recommended weight" (another minefield - I'm not going there but I'll assume your talking BMI just to nail it down) will make much more difference to your ability to perform than trying to up your FTP significantly. You say you've got a solid fitness base, which implies you're already doing regular exercise, so you need to look at your nutrition and maybe make some changes there. The trick will be to maintain your power while losing weight.
I was in a similar position a few years ago, where I was active ex-rugby player prone to popping on the pounds. I bit the bullet,managed my calories and over the course of a year dropped from a 16+ stone 'heavy unit' to a *ahem* 12.5 stone racing-snake. The big lifestyle change was food intake, but the turbo/rollers helped maintain my power output (shunting16 stone around the hills of mid-Hants took some effort!) and burn off a few calories. Like Citius said, for this longer efforts at lower intensity will likely help more here.
In terms of using your turbo with TrainerRoad, don't forget that your power output is based on an estimated speed-power curve ('virtual power') for your model of turbo, which can be out significantly. This isn't a big problem as you should be interested more in changes in your power rather than absolute numbers.
To spot changes, it's important to keep your setup as consistent as possible. Having the numbers bouncing around makes spotting any improvements more difficult. Tyre pressure and tyre/resistance-unit pressure are the critical factors, so check and adjust your tyre pressure to the same value every time before attaching to the turbo. Also try and apply the same pressure between resistance unit and wheel. This will depend a lot on the mechanism used to lock the resistance unit against your wheel, but do the best you can. Ambient temperature can also make a difference. In my experience it's not huge compared to the first two factors, but this could depend on the type of turbo.
If you need better absolute numbers, then you'll have to invest in either some form of power measurement on your bike (powertap wheels, vector pedals, SRM crank etc) or a power-measuring turbo (Kickr/Bkool/I think Tacx now do one). Even then, regular calibration is essential.