800 cc silicone implants sub muscular. This is what I look like now. (Photo)

You have a difficult breast shape to start with, so the outcomes will be proportionate to your preoperative anatomy.  If you have a reasonable understanding of what to expect that would be important.  Your wish picture is not going to accurately depict what you should be expecting.  You should not be nervous, but you must be realistic. 1.  You do not like your breasts. 2.  Surgery will improve the shape and volume.  3. You should have an outcome that is consistent with your preoperative condition is the surgery is performed by a surgeon with adequate skill and training to deal with difficult breast anatomy.  Check their photographs and see what they can do with your starting point.

Based on your photos- you are a candidate for mastopexy and augmentation with implants ( preferably silicone) with  sub-muscular placement with no more than 350cc. In my opinion- you are not a candidate for 800cc implants with sub muscular placement. Crescent lift- in my opinion- is not going to do much for you based on the photos provided. 

Big implants are big problems.  Add a lift to the mix and you are set up for complications.  Some doctors in this forum may be more courageous than me, but most I think would take my position.  I'd like to read other responses.

Thanks for the pictures and question! I am interested what my online colleagues would say, but in my humble opinion I am also nervous about your surgical plan. I think an 800cc implant is probably too large for you. Additionally, I do not believe a crescent lift is the best option to correct your asymmetry and nipple position. I think it would be worth having a second opinion with a board certified plastic surgeon to be sure. If the second surgeon has the same plan at least you will be less nervous. Just for some perspective, I have attached before and after pictures of a patient of mine that had slightly more ptosis, but a similar body type and breast size. These are 420 filled to 460cc saline implants with a lollypop lift. Best of luck!

Realistically you are not going to go from where you are now to the breast look you are expecting. Regardless of breast implant size you have, you have a breast sagging/deflation issue which is going to be further magnified the bigger the breast implants get. Adding a crescent nipple lift at the time of the implants will not help and will just end up with a wide upper areolar scar. You should manage the breast sagging first and then have implants of that size placed. This will give the best result.

Based on your photos you have a short distance between the nipple to the IMF. This may be a limiting factor for you. The possibility for a double bubble is high. Consider getting a smaller implant and with time your skin will stretch. You will also know if you are OK with having such large implants as 800 cc placed in the future (back problems?)

Thanks for your question and posting your photos.  Your situation would be very beneficial to others on this forum.  Based on your photos and the plan you presented, I would be nervous too.