Welcome to the microwaves. I would not be too worried. I have used an SG labs transverter in combination with an FT-817 on 23cm and found the results to be surprisingly good.
If you are using an IC-7100 then as you have already discovered, the main issue you will have is with reducing the max 50 watts at 144MHz to a level suitable for the transverter. Andy G4JNT gave excellent advice in an earlier thread on how to use an oscilloscope and simple RF probe to check for an initial power surge as the rig's ALC kicks in to reduce the power to your desired level. The FT-817 is popular as a transverter driver because it is a QRP rig and therefore there is less chance of putting out a bad signal or - just as importantly - frying your transverter due to equipment malfunction or just twiddling or forgetting to twiddle a knob.
If you are going to run the SG Labs transverter barefoot (ie 2 watts) then obviously the scope for being a nuisance on the bands is much reduced. I doubt anybody will be concerned about your signals at all unless you are very close to another station.
If you are running into a high power amplifier then you need to take greater care. But please don't let these discussions put you off. Most of the complaints about modern VHF rigs are related to high power use on 2m and sometimes 70cm. By the time you get to 23cm, you are in much safer territory from a poor Tx point of view. Obviously it depends on your location, but most of the time you'll find you can't hear anybody at all on the bands at all unless you are pointing your antenna directly at them or they are pointing directly at you.
And most microwavers are incredibly helpful people who want to encourage activity on the bands, so if you run into trouble on the uW bands, you are much more likely to receive offers for help rather than a grumble. If they only had an IC-7100 and an SG labs transverter available, I think that most experienced microwavers would put their combo on the air and check with neighbours etc. to see how it sounds.
So my advice is to get on the air and use it as an opportunity to learn. Hope to hear you on 23cm soon.