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Q1 Your wife is eligible to apply for a Visitor visa in the usual way up to 3 months before the planned travel date. https://www.gov.uk/standard-visitor-visa
Q2 IMHO since you already have your visa she has the option to apply now or wait until you are actually in the UK. Since youβll be travelling pretty soon, it might be better to wait.
Q3 A letter from you supporting her application is essential, without this she has no demonstrable premise for the visit. There is no standard format. This question should help you compile one What details should a good cover letter contain to back up a UK Visit Visa application?
Q4 Your wife needs to be very careful to present herself as a genuine visitor (see V4.2 of the Immigration Rules https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules). Showing that she can continue working while visiting the UK for a reasonably extended period undermines somewhat the case that her job is a tie to home / compelling reason to return and therefore an ECO might view it as an indicator of an intention to overstay. Note however, that working remotely while visiting is not against the Rules in itself Where can I travel for prolonged periods of time while legally working remotely for a company in my home country?
Q5 Yes, you should provide your landlordβs approval along with other relevant supporting documents such as your wifeβs bank statements, employment contract etc https://www.gov.uk/government/publications/visitor-visa-guide-to-supporting-documents/guide-to-supporting-documents-visiting-the-uk