Hello and welcome to the forum,
There are a couple of differently priced solutions for lifelines; but regardless you will need a pullpit--the railing that wraps around the bow and keeps on on board. The attachment is a measuring form you can use to define the dimensions of your pullpit. Or, most any marine stainless shop or canvas shop will have a similar form. Depending on where you live it would be better to find someone local that can come out to your boat and do the measuring.
You can live without a pushpit--the railing at the stern of the boat--and just bring your lifelines down to terminate near the stern cleats.
Gates: You can get by without gates and just step over the lifeline. Gates as stanchions are fairly standard. I like Garhauer's work a lot. Their welding is first rate and they are extremely reasonably priced. Here is a link to their catalog to the stanchion gate page. http://garhauermarine.com/catalog_process.cfm?cid=56
Remember when selecting gates and stanchions to use around a 5 degree offset from vertical to account for the camber of the decks.
This should give you a start at pricing out a lifeline system. As to mounting the stanchion bases, If you look underneath the side decks you can see the general area where the old stanchions were--the cabintop liner will be cut out from those areas. I would use those same areas to reduce the complexity of the job.
Click here to view the attachment