Sure! Windermere, Keswick, and Dumfries are definitely worth visiting.
Here are some travel tips for your proposed visit:

Best Time to Visit:
The ideal times to visit these places in the UK are Spring (April and May) and Autumn (September and October) when the weather is typically pleasant. In terms of crowd, July and August are the busiest months.

Route and Accessibility:
Windermere is easy to get to by train from Oxenholme Lake District on the main line from London Euston. You can get around the Lake District with public transport, or even better, on foot or by bike. Keswick is a 30-minute drive from Windermere. To get to Dumfries from Keswick, you can drive which takes approximately 1 hour and 38 minutes via A7.

Altitude and Acclimatization:
These places are not at high altitudes, hence acclimatization is not a concern here.

Accommodation and Booking:
Considering they are popular tourist destinations, it is advisable to book your hotel accommodations in advance. You can find accommodations ranging from luxury hotels to B&Bs, campgrounds and vacation rentals.

Clothing and Essentials:
The weather can change quickly in the UK so it's best to bring layers. Expect rain and pack a waterproof jacket. Don’t forget a good pair of walking shoes, a hat and sunscreen.

Health and Safety:
General standard travel precautions should be sufficient. In terms of safety, these areas are generally safe, but it is always sensible to keep an eye on your belongings.

Local Etiquette and Respect:
The locals are generally welcoming and friendly. It's important to respect the environment especially when hiking in the Lake District. Stick to the footpaths, leave no rubbish behind and keep dogs on a lead around wildlife and livestock.