Any plugins to add drop down for selecting template?
Short answer – no, there isn't any way to add a dropdown for template selection to Sections without modifying the core (which is never a good idea).

Beyond that, its difficult to advice without a brief description on what you're attempting to build. Craft is generally perfect for flexible, modular content and layouts, and what you want to achieve is most likely very doable – but I suspect your approach may be a little misguided.

Sections in Craft are the basic containers for your content, and creating a whole new Section should never be part of the basic editorial workflow.

If the OP provides a little bit more context, I'll try update this answer with a suggested approach.

EDIT:

Your problem is that you're using Singles – one of three possible Section types – as entries in a stream of content (events). This is not a feasible workflow. Singles are meant as one-offs; completely unique bits of content that doesn't fit anywhere else and needs its own, unique field layout and/or template.

Any content that is part of a stream, such as a blog post, news item or event listing should be published as actual entries to either a Channel or a Structure Section (in your case I'd use Channels for both news and events; the latter is only appropriate if you need to nest entries or put them in a specific order).

Using a Channel or Structure means that whatever template you specified when you created the Section will be automatically loaded for all its individual entries, and your client will also not need to re-create the field layout every time they want to publish something.

Obviously, with Craft Personal edition, you're limited to only one Channel – and you specifically need two. You have two options:


Upgrade to Craft Client/Pro. If you want to test it out before purchasing, see this page for info.
Delete the News channel and create a new, generic channel called "Content" or the like. Create two different Entry Types for the channel, called "News" and "Events". This would enable you to create different field layouts for news and event entries. In your channel's entry template, you could then do something like this:

{% if entry.type == 'event' %}
    {% include 'event.html' %}
{% else %}
    {% include 'news.html' %}
{% endif %}


Note that this solution will not really scale well at all, and the editorial workflow would also be subpar compared to having separate channels. I'd strongly recommend the first approach :)

Finally, I'm not familiar with ProcessWire and couldn't advice which is better for your specific project, although your site would be a doozy to set up in Craft – as long as you apply its concepts and tools the way they're meant to be used. Obviously, if you're coming from ProcessWire or any other CMS (like Wordpress or ExpressionEngine) it can take a little time to adapt to a different terminology, toolset and workflow and to absorb platform best practices. I'd advise you to read through the basic docs (they're quite concise) for a better understanding of how Craft manages content, and to give Craft Client or Pro a test run before deciding.