My DTRs are one of my joys. I have 2 and a parts machine. Unfortunately I only have 1 keyboard which is fully working properly, and no spare pens. My batteries won't hold a charge either. You can have them replaced by companies such as "Batteries R' Us", but they're expensive, like most LTs. The DTR takes an ordinary 12v adapter, the original wasn't very good anyway. Allegedly prone to failure, and according to some, could take your DTR with it. The keyboard socket is a regular PS/2 one, so you could use that until you found a mini. It also has an ordinary VGA socket if you should want to use a bigger monitor at times.
The pen, which is battery-powered can be replaced with a Fugitzu one. It has normal parallel and serial ports so you can use a seral mouse until you get one. The HP Kittyhawk drive has limited memory by todays standards. One of the solutions is a micro-drive such as were used in the IBM notepad, now taken over by Fujtzu. Another, since the HDD interface is PCMCA capable, is to get an adapter(readily available and cheap) and rig a CF drive.
I do have a plethora of fdds, not sure about my cable abundance, which I could sell you.
Zane Healy, a guy who's regular in Vintage circles, once had numerous DTRs. He posted several times in the Yahoo DTR forum, which is now largely moribund but has a lot of info in it's archives. You might get his emal address there. You'd have to join of course.
One of the downsides is that MS$ in it's wisdom never made available a Pen driver for W95, even tho it developed 1, but left it up to individual manufacturers to support. That means if you wan't to upgrade to a newer OS you'll lose the Windows Pen capabilities. There is a Pen driver available for OS2 and I've been meaning to install OS2 Warp4 on one of my DTRs.
At the moment my DTR rig is anythng but small. In the field I have a heavy 12v battery pack originally used for "Weed-Eaters". In the car it's no problem, a straight-thru adapter supples power thru the cigarette lighter. I have a 12v MicroSolutions "BackPack" CDrom with an ESS sound-card in it to use music programs, play audio CDs, or install programs. For extra storage I have a PP Iomega Zip drive with a Zip-Unleashed small battery/w/charger to drive it. What I've been trying to acquire for some time is a serial GPS receiver like Earthmate. They were gong for about $10 several years ago all over Ebay but most sellers I found wouldn't ship it to Canada. "A pox on all such jingoists. May they get lost in bear country while hunting up here ! " :^))
Contact me for any other info or an fdd by PM.
Lawrence