Monocouche is better as it is tinted / through coloured so you don't ever need to paint it again + if you chip it or knock it it's the same colour underneath. It's also more flexible so less chance of cracking and coming off. Silicone render by Wetherby Building Systems is probably better than monocouche as even more flexible and water resistant. If it was me I'd pay a bit more and not have to worry about it anymore.

At the moment that lip is a perfect catchment place for rainwater. If the boards/cladding or whatever you choose is slightly proud of the brickwork that would also help to direct rainwater away from the base of your house. Another option is to re- render bringing the render out furnther to the same elevation as the brickwork. On rereading your question maybe a finished render over the whole of the surface would be the neatest and tie it together. The thickness difference will have to be made up though to make it look seamless.

I would be tempted to wait until you have the funds to do all the work together. However it's appearance could be improved in the meantime. I would leave the window frames if you are replacing the windows, it's a waste of your money to paint them. You could try and powerwash a small test piece of the render and see how much difference it makes. Paint is always the best budget option. I would definitely try a few test areas to decide on a colour. Some large plants in pots would really soften the exterior too and would be a lasting investment.

You have done the job backwards presumably placing windows where it suited your internal room layouts. For good design you should address the facade at the outset and adjust the internal spaces. Houses of this period had lower ceilings and shallower roof pitches. In consequence they have a tendency to look squat. Extending their frontage only exagerates this look. The way to address this is to emphasise the vertical elements. Aligning the door and window openings does this but you have altered these. Given what you have I think the best you can do is break up the facade vertically. You could add vertical cladding to the central section, where ideally the front door would be, then render either side.