Great work bumping up your FTP! 50 watts in 6 months is huge!!
Regarding questions 1 & 3, there shouldn’t be much of a difference if you switch from ERG mode into resistance, as you ultimately still have to do the work yourself. ERG will just take care of the resistance level of the trainer without the need to shift. All that’s left for you to do is pedal!
Still, some athletes insist that resistance is the way to go for them, so it wouldn’t hurt to try a couple of workouts in resistance mode to see if that changes anything for you!
While we generally advise training in the small ring up front, it may be worth shifting into the big ring if you’re preparing for a flatter course. The big ring will get the flywheel of your trainer spinning faster, which will give you more inertia as you’re pedaling, which simulates the same feeling of putting out power on a flat (or even slightly downhill) road. Some athletes find it easier to put down power on certain types of terrain more than others, so it could be worth experimenting to see if you get different sensations in the legs by training in a bigger gear combo.
If you’re using a power meter with your smart trainer, make sure that you have PowerMatch turned on. This will allow you to train using power data from your power meter while still enabling your smart trainer to control resistance. That will take care of any discrepancies that may exist between your power meter and your smart trainer, which means you’ll have consistent power data indoors and outdoors.
Outside of your indoor training, it does sound like it would be a good idea to get outdoors every once in a while! Even if it’s only once every week or two, getting in those outdoor rides can be great practice for learning what it feels like to push out the power you need to in “real world” conditions. Just make sure to choose the best routes near you to optimize your outdoor training.
Your positioning on the bike will make a difference as well. It’s important to train in the position you’re going to race in – so in this case, it sounds like an aero/TT position. If you don’t practice holding that position while putting out power in training, it can be difficult to do so on race day.
Finally, consider the effects that the race itself may have had on you. It’s tough to compare a bike workout you did while fresh to a bike leg from a triathlon coming right off of the swim. If it’s possible, adding in some brick workouts to your training routine could help you nail your transitions.
Also remember that external conditions (weather, wind, terrain, etc.) can add up as well. If your race was hot, for example, it could be a sign that you need to dial in your hydration/nutrition for these long events.
Overall, as you said, it sounds like it was a great learning experience! Big kudos on getting back out there after 2 years, and hope to see another race report from you in the future!