I presume that your web application is in perl; if so, then using perl for scripting needs no additional resources. Personally, I do not understand the disadvantages of option 2. What is wrong with having the power of perl at your disposal? Training will be needed in any case, whether it is perl or your custom language, and I suspect that admins would be more willing to learn a language that is useful for other things than a single use custom language.

But suppose you don't buy this argument. I would look first to Template Toolkit and/or Mason for ideas on how to implement your little language and integrate it with HTML.

If those are not extendable to your needs, then a full parser is in your future. First, you will have to create a language and forge a grammar that has no pathologies and is unambiguous. P::RD is a good choice for the parser, as there are many example grammars out there to learn from. Another choice is to create your own top-down parser. Nonterninals are mapped to subs, terminals to regexes, and translation can either be done as you parse, or later walking the parse tree.

Whether you use P::RD or roll your own, you will want to learn how to create good grammars, handle variables and symbol tables and detect all manner of syntax errors. The best book I know of for these tasks is Compilers: Principles, Techniques and Tools, by Aho, Sethi and Ullman.