Website Re-Optimisation and Repair

I am not looking to change the design / template for my website. I like the design and format, but I have also noticed several glaring errors and time is not on my side to bring this up to speed.

I want to get the website to a good place reducing page and site errors and then to also look at what needs to be done moving forward to improve analytics and SEO.

For example, I ran several checks on the site today and returned the following scores / information:
WooRank 60/100
Nibbler 6.5
Website.Grader 77/100
SiteChecker: Paghe Score 0/100
SEMRUSH: 77% (35 Pages with Issues out of 49)

Link for Website.Grader for example: https://website.grader.com/results/www.merciaits.co.uk
SEM RUSH Report:
• Healthy (7)
• Broken (4)
• Have Issues (35)
• Redirects (3)
• Blocked (0)
Errors: 40
Warnings: 519
Notices: 76

Whilst I am ok building the basics and trying to maintain the site - obviously I have hit a stumbling block with making it right.

The quote I would like initially is to "FIX" the website and if this also includes initial SEO (YOAST) set-up, then this is perfect. I am happy to discuss a monthly service AFTER this initial project.

Website: www.merciaits.co.uk

** NOTE - DO NOT CONTACT ME DIRECTLY VIA THE WEBSITE / EMAIL - YOU WILL BE IGNORED & BLOCKED **