Let me start with
masternode.
A physical network node is an active electronic device that is attached to a network, and is capable of creating, receiving, or transmitting information over a communications channel. Here electronic device can be even raspberry pi or virtual private server.
1. If you want to run masternodes of multiple currencies, you don't need to have multiple commuters for that. You can use multiple droplets of
digitalocean,
vultr,
google could. That eliminates demands of multiple devices because each of droplets or instances will have unique static ip.
2. Yes, if you have large amount of coins that you want to put them as collateral for mn's, you can setup multiple masternodes of same coin.
3. There is absolutely no problem for having wallet in same computer.
4. You should always look for circulation supply, volume, development and community engagement for choosing any types of masternode. You should avoid mn with ROI of 7-15 days. Instead, research established projects those are having masternode implementation in their roadmap like WaBi, Block Array etc.
Hope your all queries are cleared.