Autopilot is a big no with DOF. Yes, there were autopilot systems available back then, but the Il2 Autopilot is not really a proper model of these. It simply hands control to the program which then encounters modded FMs it was never designed for.
The AI have the same problems and writing FMB missions includes a fair amount of AI testing to get them to follow the right path. They do in the end though, because every facet of the waypoints can be programmed. But human pilots have to be hands on.
The Level Stabiliser is possible to use, and is closer to actual autopilots of the time IMHO.

The Neiuport 28C1, by 101tfs, is one of the most beautiful models we have in DOF. The prop is biggish, but a problem? I don't see any.

I also found the little Neiuport very difficult to break, reaching 170mph in a dive and recovering easily from breakaway in high G turns as well.

May I suggest you look at the 'Difficulty' Settings. There are a bunch of new 412 features that introduced: 'Torque and Gyro Effects' and 'Flutter Effects'. These options are fine for WWII stock gamers but have a detrimental effect on modded WWI Flight Models. Turn them OFF from the 'Difficulty' settings at QMB, or in FMB. I find that Difficulty settings are easiest to access from QMB and once set will stick to the rest of the sim until changed again.

If you have a different 3D to the pictures or some other problem has crept in that I can't replicate I can tell you this with confidence - Of course we can fix it, we can fix anything!

We do have the SPAD SVII - This beautiful example by Kant, with extra textures by vpmedia. I don't know of any XIII project currently but if you find one please send me a link!