Scanning is much like printing in that its a layer where compensatory brightness/exposure control may be applied.
See
Exposure - Exposed! your comment on first pic is the reveal. 'You' think its a bit over exposed; b-u-t, you have a white house with a white wall behind it. IF you had been using a hi-er-fi camera good odds that a coupled CWA TTL exposure meter would have averaged that out and pulled down the exposure a bit. What you have is more akin to what you might have got using a hand held 'incident' metering, which would have looked at the brightness of the light falling on the scene, rather than the light reflected off it, and without and averaging out of bright areas of reflection, let them blow a bit. In which case yeah, it could 'seem' a little over exposed....
B-U-T... as tut, thing is there is no such thing as a 'correct' even less 'perfect' exposure, merely one you like or don't! And as tut, for an exposure that by whatever method is metered as 'correct' you probably have two or three stops either side of that, where the resultant picture is more of less to your taste, and probably a couple of stops more before you start loosing image.
To 'me', I don't think that this film ASA or 'push/pull processing milarky, is either a relevant or an issue. Using these lo-fi or 'Toy' cameras with such restrictive control, is what before some Austrian Students slapped a brand name on it and called it 'Lomo', we called 'Serendipity Photography' Happy-Chance picture making! Where fixed aperture/shutter lo-fi cameras clipped the extremities and forced a 'constant' into the equation, and made you concentrate on the scene and framing, and just getting a shot, rather than messing with settings getting bogged down in the technicalities.
Shots as shown, then, to my eye are rather soft, as you'd expect from a probably plastic lens toy-camera, and are lo-fi charming from it. And probably wouldn't be any more pleasing by dint of a better centred or scientifically 'correct' exposure.
Two and a bit things to ponder. Worrying about exposure from these cameras then you may be chucking the baby out with the bath water, and loosing that lo-tech antique 'feel' for some idea of 'better' that is more oft associated with 'fancy' cameras with meters and settings that more often inherently deliver that higher level of clinicity, and next, two or three stops, 'diddleability' you may have in processing, for a whole roll; you cant adjust the film speed frame by frame and you cant push/pull process individual frames on a roll, a-n-d, its 'only' two or three stops, when you likely have over a dozen stops of 'exposure latitude' and six-stops 'range' in which you get a pretty good exposure and the 'best' exposure is just the one you like best. In that the merits of push/pull processing are first of little significance, a-n-d a skew solution to what is probably not a problem. Pushing/pulling to effect 'some' adjust-ability on the film speed, where you lack adjust-ability on the aperture/shutter, is rather perverse, especially when, as said, you cant really effect that adjust-ability frame by frame, like you might if you had an aperture/shutter control, and it is still a relatively small amount of adjust-ability compared to the range you are working in.
As said, If you want 'better' than these lo-fi cameras are capable of, the answer is to take you into hi-fi cameras, with variable aperture/shutter controls, and up into metering methods where you start to get a lot more prosaic about the job, with or without the aid of an in camera computer to do the maths and even make the settings for you... the conclusion of which is to use a high-end modern DSLR, with a hand held accessory light meter.. and the 'baby' is well and truly inspecting The Water-Boards tomato plants whilst you faff with the settings! Your call!
