Definitely! Here are some valuable travel tips for your planned journey:

Rome, Florence, Venice:
Best Time to Visit:
The best time to visit Rome, Florence, and Venice would be in the shoulder seasons of April to June and September and October. Weather is typically more mild and attractions less crowded.

Route and Accessibility:
Trains are the easiest and most economical way to travel between these Italian cities. Renting a car is not advised due to heavy city traffic and expensive parking.

Altitude and Acclimatization:
These cities are at sea level or very close to it, so there's no need to worry about altitude sickness. However, ensure you stay hydrated in the warmer months.

Accommodation and Booking:
All three cities have a range of accommodations, from luxury hotels to budget hostels. Be sure to confirm reservations in advance, particularly during high tourist season.

Clothing and Essentials:
Pack according to the season. For a summer trip, bring light clothing, a hat, and sunscreen. Carry a reusable water bottle to fill up at the public fountains. Always remember comfortable walking shoes, as these cities are best explored on foot.

Health and Safety:
Italy is generally safe if reasonable precautions are taken. Beware of pickpockets in crowded areas. Keep a digital copy of your passport, and crucial documents.

Local Etiquette and Respect:
Keep in mind that Italians appreciate good manners and respectful behavior. Dress modestly while visiting religious sites.

Barcelona, Madrid:
Best Time to Visit:
The ideal time would be April through June and September through early November. It's more mild and less crowded.

Route and Accessibility:
Spain has an efficient train system, particularly AVE trains, for travel between major cities including Barcelona and Madrid.

Altitude and Acclimatization:
Like in Italy, neither of these cities are high altitude, so altitude shouldn't be an issue.

Accommodation and Booking:
Just like in Italy, early reservations are recommended during high tourist season. If you're planning to visit during famous events like La Tomatina or Las Fallas, you should book several months in advance.

Clothing and Essentials:
Similar to Italy, pack according to the season. However, Madrid can be particularly hot in summer, ensure you carry a hat, sunscreen, and a reusable water bottle.

Health and Safety:
Spain is generally safe, but some precautions should be taken. Beware of pickpockets, especially in Barcelona.

Local Etiquette and Respect:
Remember to respect Spanish customs, such as late dining. It's also important to use formal titles until otherwise invited, and dress smart for nightlife or finer restaurants.

Happy Travelling!