Loosing SERP with redesign?

[extra]

I know many have asked before and even more have answered, but unfortunately I have not found answer for exactly this topic.

I have a 3 year old site, and searching from my own country with language specific filters my site is doing very well when looking at the SERP.
But I have 2 problems.
a) I should have learned myself som java as the site is growing and a lot of job to keep updated with HTML
b) I need to a complete redesign of the layout (menus, resolution, etc)

At the moment I'm thinking of doing this redesign and keep it as HTML. This is based on the fact that I need at least one more year before I have time enough to learn myself some Java (I have to run my business as usual besides doing this redesign).
But if I do this redisgn in HTML now I will probably have to redo the whole design within 2-3 years with Java anyway.

So, - my main concern is that I'm afraid loosing SERP if I do any of these redesigns. I was thinking of keeping my URL's and headers as they are today.

What do you suggest?
1)
Is it possible to do such redesign without loosing SERP?
2)
Is it better to wait and do the whole redesign later (with Java) in case I loose the SERP?

[smells so good]

You can phase in your changes over the next couple of years, which prevents a complete site change all at once. It's the same thing I've done with a site and my results were good. Overall SERP's have actually improved.

a complete redesign of the layout (menus, resolution, etc)

A good place to begin Phase 1. You can maintain your current url's, or 301 redirect any pages that need to change. Don't overdo the redirects. Make changes gradually, not all at once. Double check the headers on any redirects.

<aside>
I'm not a big believer in PR, however, when you redirect a page you will temporarily lose the PR on that page. It's possible that if every page on your site suddenly lost it PR, a flag could be thrown and you could be out.. for a while. (I have no proof of this, just saying it's possible) My own preferance is to let a group of pages fully recover before making the next set of changes.
</aside>

Incorporate your new layout thru the current site. If you are ranking well now, consider those on-page factors that help each page to rank, and incorporate them into new layout. This would be a good time to double check each page for valid markup and unique/relevant meta tags. Add style sheets if needed. IMO, changes that improve usability vs SEO changes, will not cause your pages to lose any significant ranking.

You might want to test a small group of pages before you commit all of your changes. Phase 2 can begin after you learn java, and you would generally follow the same process.

[extra]

Thanks for your information.
The sita have now about 160 pages. How many do you think I can cjhange before step 2?
5?
10?

[smells so good]

That's not a huge number of pages. I'm not 100% certain of what you are planning. What I did for a similar sized site was to create a new layout and I installed that site wide. Do that part well and it shouldn't affect your SERP's.

The thing is, I was also performing redirects on all of my pages, so I wanted to make sure everything was looking good before I did the next bunch of pages (the layouts were already done). I didn't want to lose PR on all of my pages at once. I'm not sure if that would affect my SERP's, but I redirected every page - eventually - without losing any ranking, and I did mine by a handful of pages at a time. Pick a number you're comfortable with.

You said that eventually you wanted to use Java, after you learned enough. That's the second phase I was taking about.