Both the Jawa 42 FJ and Yezdi Roadster are mechanically very similiar with the only difference being some visual elements and how you sit on the bike. A test ride of both over various road conditions should help you decide which one is the right fit for you. 

Coming to when to clean your bike, that's a very subjective thing based on where you live and how you store your vehicle. If you have covered parking that protects your bike from dust, then a soap wash once every 10 days to a fortnight should be more than sufficient. If you don't, then you may have to clean it more often. 

To prevent rusting, try to regularly coat exposed metal parts with some sort of grease and try to keep them under a good-quality bike cover. 

Both the bikes you own can make for good touring partners. However, we would lean towards the Honda CB300R over the Yezdi Roadster.

Its seating position will keep you more comfortable on broken roads. The lighter weight and sprightlier performance also make it more engaging on smooth, winding tarmac roads.

Additionally, it’s worth keeping track of service centres for both bikes in the region you plan to tour, just in case you need any mechanical assistance.