You've got some issues but with a distance this short, also the backup of bus tickets, which should be available a day or two in advance. For the train:

1) Almost no agent will guarantee train tickets for the Chinese New Year period, so while throwing additional money at the problem (in the form of agent fees) is a usual winner, in this case it's likely to be a non-starter. You can try though.

2) For the fast trains (G and D), even if your have friends that can buy on your behalf, your ID is needed. I have a feeling that during this period, the train ticket offices aren't going to be satisfied by anything less than seeing the real passport. For the slower trains, which take hours longer but still run on this route, I have seen mixed reports about whether ID is needed, due to implementation (or not) of new regulations. In short, this method may also be less than fruitful. And remember to send any friend out into holiday ticket purchase situations requires a seriously nice gift or quid-pro-quo from you in return!

3) Online may be possible, if you have somebody at your end that is a reader of Chinese and can help you navigate the official website:
www.12306.cn (not .com) It is true that the confirmation you get still has to be exchanged at the station for the actual tickets but at most major stations there should be a special queue window set up for that especially at CNY time. I am not sure if there is a time limit before departure for exchange...after which the unclaimed ticket would presumably get tossed back into the availability pot. And payment requires a bank card issued by a Chinese bank, AFAIK. Either language or payment barrier may trip you up on this one.

4) If you can travel on the 24th or 25th, your chances of finding something on short notice go up. Possibly even the 23rd itself.

5) Train seats are assigned by the ticketing computer at time of purchase, so yes, if you get a ticket, your seat is confirmed. Exception: when seat tickets sell out, most trains during CNY will sell a specific number of Standing tickets for the 2nd Class (high speed) and Hard Seat (standard train) classes. These people will hang out in the space between the carriages, by the restrooms, etc. Not a great way to travel, but on the D or G fast trains, with a time of 2-3.5 hours, migh be doable. But I would think even standing tickets will sell out also. Personally, I'd go with a bus seat vs this option.