Have to add new ring circuit to an existing single ring installation. Done paper load assestment (just over 90A with freestanding electric cooker). Breaker box is a MEM brand which is almost impossible to get an extra 32A RCBO breaker for (recently bought complete Wylex breaker-box replacement)...
I having to replace basin taps and a bath/shower mixer tap for a similar reason because the splash covers are circular - mole grips will not get a purchase. The replacements have a small hex/octa section for a wrench.
Could replace rainwater downpipe with full sized soil pipe below level of the 2 waste branches as Screwfix do some rubber drain pipe adaptors for this. Not sure what discharge into gulley will be like with this set up. Do make sure gulley is connected to main soil/waste drainage sewer.
I know a competing diy firm does an air spaced cable with copper braid/core with aluminium foil shielding that will be next to useless for the F connector terminations because it will collaspe/become severely chewed.This cable has been fortunately sold (in store) only with a black sheath.
If running latest OS I would find that at least 2Gb of memory should make the system stable. Depends if memory is also shared with graphics, if so an extra graphics card would help here as it would reduce the main processor/memory loading.