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. 

The latest Classic Legends bikes have come quite a way from their predecessors in terms of build quality and finish levels. The Jawa 42 FJ, in particular, is a machine we quite liked when we rode it. 

As a machine, it is a capable option, but we haven't had the chance to test its long-term reliability yet. You should also know that the company has a less-than-stellar reputation for after-sales and servicing, so do find out what the exact situation of Yezdi/Jawa service in your area is before you go ahead with the purchase. 

While you don't want the Classic, the Royal Enfield Hunter 350 is a good option if you want something similar in feel but different (read: modern) in its design. It is also one of the more manageable Royal Enfield bikes, which should be approachable for you. We would also recommend you test ride a Royal Enfield Scram 440 because it blends old-school charm and quite a lot of modern capability. 

You can also take a look at the Honda CB350 models because they look and feel more modern than their Royal Enfield counterparts and should be easy to manage in the city.