Sounds like you have a mature attitude so good start ?
Stick to AEG for the beginning. I would say £250-£300 will get you a very decent performing & reliable BB slinger.
Have a search in the forum for recommended first weapon and best manufacturers. (Obviously there will be a lot of M4/AK but might mention things to think about like attachments etc)
Remember that all AEGs work with the same basic mechanism so the shape doesn't affect performance. Even barrel length may not guarantee better performance or accuracy. Higher quality components (cost) will generally improve performance out of the box but its not guaranteed either and there is generally a diminishing return the higher the cost.
Basically, look for the style/shape you like the look of most and then research which one to buy.
Don't rush into modifying. Its usually best to start that when you have at least 2 weapons so you have a backup.