Help. Renegotiating the price of a property after a building survey. What are the risks?

As the title suggests, we recently got the results back for a building survey. The house was priced at £210k and we got it for £207.5k. The house is in Gwynedd, it's a 3 bed semi from the 50s/60s.

I know building surveyors are on the cautious side because they have to cover their own backs and it's better to be heedful than heedless, but there are a few items in the report which concern me a little. It is standard ware and tare for a property of this vintage. They are:

• Chinmey stacks. Lead flashing is in poor condition and the stack requires repointing. Vegetation growing in the mortar cracks. Scaffolding + repointing + flashings ~1,500k?
• Roof coverings. Distorted slates to the front slope. Surveyor recommends overhauling or re-roofing. This once I'm unsure of. It seems roofs always get mentioned.
• Front porch. Suffered from structural movement, should be specified by a structural engineer, should be stitched/tied to the main house as per the recommendation in the report. Essentially secure it.
• Roof structure. Timbers around the base of the chinmey stack were wet at time of inspection following a period of dry weather. Surveyor recommends roof is recovered in a breathable membrane.
• Dampness. High readings across the walls in the entrance hall, front wall and reception room, dining room and kitchen. There is no extractor hood above the oven.
• Garden - retaining walls (landscaped garden) failing due to inadequate drainage.

Given these comments, is it reasonable to renegotiate? My concern is obviously the seller pulling the plug, I want to negotiate in good faith. I would assume the first step is to contact my/their EA and get a quote from a builder/roofer. Thoughts?