I recommend sitting down with a kitchen designer, they would be happy to guide you through the whole design process and most will do it for free.

To make the most of corner cupboards, either get a blind corner with LeMans pull out or if you're on a tight budget, stick to L shaped corner cupboards so that you can still get to the back and make the space usable rather than just available. Block your tall units together away from the window to make the most of the light and use a light coloured worktop to bounce the light into the room. If you still wanted to use colour (why have a boring kitchen) you can be bold on the base units if you keep the wall units a light colour. Using downlights on the wall cupboards will bring task lighting where you need it most and if you put them on a separate electrical circuit to your ceiling lights, they can create a beautiful atmosphere to your kitchen in the evenings.

We had a similar project and gutted the house. Rewire replaster all walls and ceilings. We restored the original parquet flooring and then new carpets everywhere else. Knocked through between kitchen and dining room, new garage roof. New doors and work surface but kept the original kitchen units. Kept the bathroom but put in a new floor. Did this for about £10k. Now 18 months later we're looking at extending the kitchen diner into a big open plan room going out the back as you have suggested but also out to the side. Our neighbours have done similar and we think we can get it done for about 30-40k not including the kitchen. The side extension means a fair bit of structural steel so if you don't do this then it saves a fair bit - our other neighbours have done this. We want an open but defined space so we're looking at keeping a pillar (also cheaper) then having an L shaped kitchen diner around a more relaxed sitting and entertaining area. The idea being that for dinner parties you mill around and have drinks in here before going to eat. Also can have friends round for coffee etc while the front living room remains the primary TV watching area. We'd keep a small boot room off the back for the dog, a pantry in the middle and a toilet at the front. See below for some pictures that illustrate our plans. These are mine and just awaiting our architects plans. In summary I'd get it up to a basic standard until you've got a bit more then go big, although as you say with your cheap labour you might get what you want for the money!

Exciting times- I think side by side ovens have more presence and the island is a great place for the microwave. I don’t like seeing a microwave high up as I think it is dangerous. In fact you should put your ovens at a really comfortable height for you. I notice all of the designs show a draining board- personally I would choose an undermounted sink and no drainer to maximise work surface. I agree about putting the extractor in a cupboard- it doesn’t have to be a 600 cupboard though- I think it looks more luxurious if it is 20cm bigger than the hob. Consider if the 70/30 fridge planned is big enough. You could have a larder sized fridge and a freezer elsewhere. All of your designs show the breakfast bar sitting in an Lshape at the end of the bar- Personally I think that you should have the stools on the long side of the island so that they can see the TV, so you don’t have to have a cheap looking metal pedestal and so the stools don’t obstruct the sofa in the TV area. You have also shown the breakfast bar in a different material- if you want to use the island for food prep it might be easier to use and to keep clean if there are no differences in height and it is all the same material. If you want variety of materials in the kitchen you might choose two different cabinet finishes- perhaps one could be textured. I noticed the glass cabinets on one design- I would be careful about their placement because of getting steamed up. Lastly I felt the the designs with lots of vertical lines made the room seem smaller and I preferred the designs with uninterrupted horizontal lines.